High gain durable anti-reflective coating

ABSTRACT

Disclosed herein are single layer transparent coatings with an anti-reflective property, a hydrophobic property, and that are highly abrasion resistant. The single layer transparent coatings contain a plurality of oblate voids. At least 1% of the oblate voids are open to a surface of the single layer transparent coatings.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the following provisionalapplication, which is hereby incorporated by reference in its entirety:U.S. Provisional Appl. 62/024,440, entitled Coating Materials AndMethods For Enhanced Reliability, filed Jul. 14, 2014 (ENKI-0009-P01).This application is a continuation-in-part of U.S. patent applicationSer. No. 14/491,259, filed Sep. 19, 2014, entitled Optical EnhancingDurable Anti-reflective Coating, which is hereby incorporated byreference in its entirety (ENKI-0008-U01). This application is acontinuation-in-part of U.S. patent application Ser. No. 14/799,223,filed Jul. 14, 2015, entitled Coating Materials And Methods For EnhancedReliability, which is hereby incorporated by reference in its entirety(ENKI-0009-U01).

STATEMENT REGARDING GOVERNMENT FUNDING

This invention was made with government support under ContractDE-EE0006810 awarded by the U.S. Department of Energy. The governmenthas certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field

The present disclosure relates generally to the field ofanti-reflective, anti-glare, barrier coatings applied to glass, metalsand plastics in surfaces, windows, windshields, screens, displays,architecture, goggles, eyeglasses, etc., in particular to glass used asthe front cover of solar modules, high-transparency glass used fordisplay purposes such as protective covers for works of art, museumdisplay glass, commercial display glass, front glass of electronicscreens or instrument panels that need anti-glare properties andautomotive glass. Specifically, it relates to soluble high silanolcontaining silsesquioxane compositions and methods for their preparationfor use as thin-film coatings.

2. Description of Related Art

The interface between air and the surface of typical glass such assoda-lime glass will reflect about 4% of normally incident light. Thisreflection is caused by the difference in refractive index of the glass,approximately 1.52 and the air approximately 1.0. In order reduce thereflection, the glass may be coated with an anti-reflective coating thathas an intermediate refractive index between about 1.25 and about 1.45.

Several methods exist to create single-layer anti-reflection coatingsusing sol-gel chemistry. Commonly used methods can be broadly sortedinto five groups. The first group: using solid silica nanoparticles havebeen known for a long time, for example U.S. Pat. No. 2,432,484 filed in1943 teaches using a solution containing colloidal silica nanoparticlesto create an anti-reflective coating on glass. Another more recentexample is U.S. Pat. No. 7,128,944 which teaches a porous SiO₂ layercreated by depositing an aqueous solution containing silica particlesthat is then sintered at temperatures of at least 600° C. The secondgroup teaches using porogenic materials to increase the porosity ofsol-gel derived thin-films. As porosity increases, refractive index isreduced. In general, porogenic materials are high molecular weightorganic compounds that create networks of small pores when they areremoved by thermal processing at high temperatures. For example,European patent application no. EP1329433 teaches usingPolyethyleneglycol tert-octyl phenyl ether (Triton) in highconcentrations as a porogen with subsequent thermal sintering thatcauses combustion of the porogen to increase porosity. A major drawbackof this approach is that the small pores created adsorb water, which cangreatly diminish the performance of the anti-reflective coating. It hasbeen recognized that one method of mitigating this problem is to createcoatings with relatively large pores. While the inner surface of thepore may adsorb water, the main void remains empty. The third groupteaches creating large pores using solid or liquid templates aroundwhich the film is formed after which high temperature processing burnsaway the template or a solvent dissolves away the template leaving avoid. For example, U.S. patent application Ser. No. 12/514,361 teachesusing particulate (quasi)spherical nano-particles composed of polymethylmethacrylate (PMMA) or nano-droplets of an oil as a pore forming agentthat templates a large pore and that are removed either by washing witha solvent such as THF at low temperature or are preferably burned awayat high temperature. The fourth group is a variant of the third, in thata solid polymer nano-particle is used to template a void. However, inthis case, sometimes referred to as core/shell, the nano-particle iscoated in a shell of, for example, silica before being embedded in amatrix material. High temperature is again used to burn out thenano-particle polymer core or template to leave a void behind. Forexample, U.S. patent application Ser. No. 12/438,596 teaches coating asubstrate using hollow particles in a binder and then curing to createan anti-reflective coating. The last group is again a variant of thetemplate method, however in this case hollow silica particles are formedthat already have an internal void, that are then embedded in a matrixto form a porous coating. For example, PCT patent application no.PCT/JP2013/001114 teaches a method of producing hollow particles withlittle or no aggregation and then producing an anti-reflection coatingusing those particles.

Many commercially available anti-reflective coating materials for theglass and photovoltaic solar module industries utilize these or similarmethods. Notwithstanding that some art teaches using a solvent to removepore-forming agents at low temperatures, this is not generally apractical method at industrial scale as it is slow and requires largequantities of organic solvents. It is therefore common in industrialscale applications of these coating technologies to use a hightemperature sintering or curing step at between 400° C. and 750° C. Asthis processing step is also commonly used as a tempering step tomechanically strengthen the glass, both processes are accomplished atthe same time.

Anti-reflective coatings that are cured during the glass temperingprocess or by other similar high temperature processing share a numberof common features. First, they are hydrophilic or super-hydrophilicwith water contact angles as measured by a goniometer of less than 60°and less than 20° respectively. The high temperature oxidizes allorganic components of the coating, leaving behind almost pure silica.Second, they are frequently quite brittle. Their mechanical strength isderived to some extent by sintering of the coating, too much sinteringreduces the coating's porosity and, hence, optical performance.Therefore, a balance must be achieved between optical and mechanicalperformance that frequently leaves the mechanical performance at lessthan ideal. In general, these brittle hydrophilic coatings are prone todegradation caused by soiling and abrasion when subject to long-termexposure to many outdoor environments.

It would be desirable to make coatings with large pores and high opticalperformance and abrasion resistance at a practical, low temperatureprocess at industrial scale that does not require solvent removal andyet still imparts good mechanical properties while preserving organicelements and properties in the coating such as hydrophobicity oroleophobicity.

SUMMARY OF THE INVENTION

An object of this disclosure is to provide a coating composition whereinthe cured film has high light transparency, low light reflection, goodmechanical properties, and sufficient weather resistance and durabilityto withstand prolonged outdoor exposure. Another object is to provide anarticle coated with said composition.

Aspects of the disclosure provide a method for synthesizing a siloxanepolymer with a composition having the following formula, the compositionhaving the following a formula, and coatings made from dried gels of thefollowing formula:

[RSi(OH)₂O_(0.5)]_(a)[RSiO_(1.5)]_(b)[RSi(OH)O]_(c)[R′Si(OH)₂O_(0.5)]_(m)[R′SiO_(1.5)]_(n)[R′Si(OH)O]_(p)[SiO₂]_(W)[Si(OH)O_(1.5)]_(x)[Si(OH)₂O]_(y)[Si(OH)₃O_(0.5)]_(z)where R is independently methyl or optionally substituted orunsubstituted C2 to C10 alkyl group, a substituted or unsubstituted C3to C20 cycloalkyl group, a substituted or unsubstituted C1 to C10hydroxyalkyl group, a substituted or unsubstituted C6 to C20 aryl group,a substituted or unsubstituted C2 to C20 heteroaryl group, a substitutedor unsubstituted C2 to C10 alkenyl group, a substituted or unsubstitutedcarboxyl group, a substituted or unsubstituted (meth)acryl group asubstituted or unsubstituted glycidylether group, or a combinationthereof; R′ is a fluorine substituted C3 alkyl group or optionally C4 toC10 alkyl group, a fluorine substituted C3 to C20 cycloalkyl group, afluorine substituted C1 to C10 hydroxyalkyl group, a fluorinesubstituted aryl group, a fluorine substituted C2 to C20 heteroarylgroup, a fluorine substituted C2 to C10 alkenyl group, a fluorinesubstituted carboxyl group, a fluorine substituted (meth)acryl group, afluorine substituted glycidylether group, or a combination thereof; and0<a,b,c,w,x,y,z<0.9, 0≦m,n,p<0.9, and a+b+c+m+n+p+w+x+y+z=1.

In some embodiments the siloxane polymer is formed from acid hydrolyzedalkoxysilanes, organosilanes and optionally organofluorosilanes, whereinthe organosilane and the organofluorosilanes are each separatelyprepared by hydrolyzing in the presence of a hydrolysis acid catalystand a solvent, such as a polar organic solvent, in a first step beforecombining with an alkoxysilane in a second step.

In some embodiments, the siloxane polymer A is formed from acidhydrolyzed alkoxysilanes, organosilane, and organofluorosilane, whereinthe hydrolyzed organosilane and the hydrolyzed organofluorosilane areeach separately prepared before combining with each other and withalkoxysilane or with another reagent.

In an embodiment, the siloxane polymer is formed by hydrolyzing at leastone organotrialkoxysilane or tetraalkoxysilane in the presence of acidcatalyst in a polar solvent followed by reacting the resulting highlybranched high silanol containing siloxane polymer with tetraalkoxysilaneor organotrialkoxysilane.

The siloxane polymer may have a relative weight percent ratio oftetraalkoxysilane to a total of organosilane and organofluorosilane ofabout 0.2 to about 2.

The alkoxysilane may be selected from a group consisting oftetramethoxysilane and tetraethoxysilane.

The organosilane may be selected from a group consisting oftrimethoxysilane, triethoxysilane, methyltrimethoxysilane,methyltriethoxysilane, n-propyltrimethoxysilane,n-propyltriethoxysilane, iso-propyltrimethoxysilane,iso-propyltriethoxysilane, n-butyltrimethoxysilane,n-butyltriethoxysilane, iso-butyltrimethoxysilane,iso-butyltriethoxysilane, 3,3-dimethylbutyltrimethoxysilane,3,3-dimethylbutyltriethoxysilane, pentyltrimethoxysilane,pentyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane,heptyltrimethoxysilane, heptyltriethoxysilane, octyltrimethoxysilane,octyltriethoxysilane, n-decyltrimethoxysilane, n-decyltriethoxysilane,dodecyltrimethoxysilane, dodecyltriethoxysilane,cyclopentyltrimethoxysilane, cyclopentyltriethoxysilane,cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane,phenyltrimethoxysilane, phenyltriethoxysilane, vinyltrimethoxysilane,vinyltriethoxysilane, allyltrimethoxysilane, allyltriethoxysilane,acetoxymethyltrimethoxysilane, acetoxymethyltriethoxysilane,acetoxyethyltrimethoxysilane, acetoxyethyltriethoxysilane,(3-acetoxypropyl)trimethoxysilane, (3-acetoxypropyl)triethoxysilane,acryloxymethyltrimethoxysilane, acryloxymethyltriethoxysilane,(3-acryloxypropyl)trimethoxysilane, (3-acryloxypropyl)triethoxysilane,methacryloxymethyltrimethoxysilane, methacryloxymethyltriethoxysilane,(3-methacryloxypropyl)trimethoxysilane,(3-methacryloxypropyl)triethoxysilane,(3-glycidylpropyl)trimethoxysilane, (3-glycidylpropyl)triethoxysilane.

The organofluorosilane may be selected from a group consisting of(3,3,3-trifluoropropyl)trimethoxysilane,(3,3,3-trifluoropropyl)triethoxysilane,dodecyafluorodec-9-ene-1-yltrimethoxysilane,dodecyafluorodec-9-ene-1-yltriethoxysilane,(heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane,(heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane,3-(heptafluoroisopropoxy)propyltrimethoxysilane,3-(heptafluoroisopropoxy)propyltriethoxysilane,hexadecafluorododec-11-en-1-yltrimethoxysilane,hexadecafluorododec-11-en-1-yltriethoxysilane,nonafluorohexyltrimethoxysilane, nonafluorohexyltriethoxysilane,pentafluorophenoxyundecyltrimethoxysilane,pentafluorophenoxyundecyltriethoxysilane,pentafluorophenyltrimethoxysilane, pentafluorophenyltriethoxysilane,(tridecafluoro-1,1,2,2-tetrahydrooctyl)trimethoxysilane,(tridecafluoro-1,1,2,2-tetrahydrooctyl)triethoxysilane,perfluorooctylphenyltrimethoxysilane,perfluorooctylphenyltriethoxysilne,heptadecafluorodecyltrimethoxysilane,heptadecafluorodecyltriethoxysilane,(1H,1H,2H,2H-tridecafluoro-n-octyl)trimethoxysilane,(1H,1H,2H,2H-tridecafluoro-n-octyl)triethoxysilane,(1H,1H,2H,2H-nonafluorohexyl)trimethoxysilane,(1H,1H,2H,2H-nonafluorohexyl)triethoxysilane,3-(pentafluorophenyl)propyltrimethoxysilane,3-(pentafluorophenyl)propyltriethoxysilane.

In an aspect, the alkoxysilane may be tetramethoxysilane, theorganosilane may be methyltrimethoxysilane, and the organofluorosilanemay be trifluoropropyltrimethoxysilane.

In an aspect, the alkoxysilane may be tetraethoxysilane, theorganosilane may be methyltrimethoxysilane, and the organofluorosilanemay be trifluoropropyltrimethoxysilane.

In an aspect, the alkoxysilane may be tetramethoxysilane, theorganosilane may be methyltrimethoxysilane, and the organofluorosilanemay be (tridecafluoro-1,1,2,2-tetrahydrooctyl)trimethoxysilane.

In an aspect, the alkoxysilane may be tetraethoxysilane, theorganosilane may be methyltrimethoxysilane, and the organofluorosilanemay be (tridecafluoro-1,1,2,2-tetrahydrooctyl)trimethoxysilane.

The siloxane polymer may be 0.1% to 10% by weight of the total coatingcomposition. The siloxane polymer may have a weight average molecularweight (Mw) of 600 to 10,000 Daltons. The siloxane polymer may include10 to 60 mol % Si—OH groups as established by Si-NMR.

The hydrolysis acid catalyst may be selected from a group consisting ofhydrochloric acid, nitric acid, sulfuric acid, phosphoric acid,methanesulfonic acid or acetic acid in amount of 0.01% to 1.0% by weightof the total coating composition.

The solvent may include water and at least one other organic solventselected from a group consisting of alcohols, esters, ethers, aldehydes,and ketones such as methanol, ethanol, 1-propanol, 2-propanol,1-butanol, ethylene glycol, propylene glycol, ethyl acetate, ethyleneglycol, foramide, dimethylformamide, N-methylpyrrolidinone, propyleneglycol methyl ether, 1-methoxy-2-propanol, propylene glycol, propyleneglycol methyletheracetate, acetone, cyclohexanone, methylethylkeone,N,N-dimethyl acetamide, dimethylether, diethylether, 2-butanol,2-butanone, tetrahydrofurane, 1,2-diethoxyethane, diethyleneglycol,triethyleneglycol, 1,2 dimethoxymethane dipropylene glycol monomethylether acetate, propylene glycol, diamyl ether, diethyl oxalate, lacticacid butyl ester, dibutyl ether, 1-pentanol, dimethoxy ethane,1-hexanol, 1-heptanol, ethylene glycol, gamma-butyrolactone, triethyleneglycol and methyl t-butyl ether, wherein the amount of solvent is fromabout 50% to about 99.5% by weight of the total coating composition.

In embodiments the ratio of organic solvent to water is between about 1to about 50 or between about 5 to about 10.

In some embodiments, additives such as high-boiling-point porogens,nano-fillers, adhesion promoters, base condensation catalysts (alsoknown as Si—OH condensation catalysts), thermal radical initiators,photo radical initiators, cross-linkers and surfactants and others maybe used in the coating composition.

The high-boiling-point porogen or template may be selected from thegroup consisting of ethylene oxide, propylene oxide, polyethyleneoxides, polypropylene oxides, ethylene oxide/propylene oxide blockco-polymers, polyoxyethylated polyoxypropylated glycols, fatty acidethoxylates, ethylene glycol esters, glycerol esters,mono-di-glycerides, glycerylesters, polyethylene glycolesters,polyglycerol esters, polyglyceryl esters, polyol monoesters,polypropylene glycol esters, polyoxyalkylene glycol esters,polyoxyalkylene propylene glycol esters, polyoxyalkylene polyol esters,polyoxyalkylene glyceride esters, polyoxyalkylene fatty acid, sorbitanesters, sorbitan fatty acid esters, sorbitan esters, polyoxyalkylenesorbitan esters, polyoxyethylene sorbitan monolaurate, polyoxyethylenesorbitan monostearate, polyoxyethylene sorbitan tristearate, andsorbitan ester ethoxylates such as TWEEN 80, TWEEN 20, PEG 600, PEG 400,PEG 300, or PEG-b-PPG-b-PEG in an amount of 0.0% to 5% by weight oftotal coating composition.

The nano-filler may be selected from the group consisting of colloidalsilica, hollow silica nano-spheres, polymer beads, polylactic acid,polyvinylpyrrolidone, polymethylmethactrylates and polyacrylates, carbonnanotubes, or Buckminsterfullerene C₆₀-C₇₀ in an amount of 0.0% to 5.0%by weight of the total coating composition.

The adhesion promoter may be selected from the group consisting of(meth)acryloxypropyl trimethoxysilane, (meth)acryloxypropyltriethoxysilane, (meth)acryloxypropyl dimethylmethoxysilane,(meth)acryloxypropyl methyldimethoxysilane, 3-glycidylpropyltrimethoxysilane, 3-glycidylpropyl triethoxysilane, 3-glycidylpropyldimethylmethoxysilane, or 3-glycidylpropyl methyldimethoxysilane in anamount of 0.0% to 5.0% by weight of the total coating composition.

The base condensation catalyst may be selected from the group consistingof alkali metal hydroxide, amide, amines, imidazolines, potassiumhydroxide (KOH), sodium hydroxide (NaOH), cesium hydroxide (CsOH),ammonium hydroxide (NH₄OH), tetramethyl ammonium hydroxide (TMAH),formamide (FA), triethyl amine, trimethyl amine, dimethylformamide(DMF), N-methylpyrrolidinone (NMP), N,N-dimethyl acetamide (DMA),thermal base generator (TBG) or tetramethoxymethyl glycoluril(PowderLink 1174) in an amount of 0.0% to 1.0% by weight of the totalcoating composition.

The thermal radical initiators may be selected from the group consistingof azo compounds and peroxides such as 4,4′-Azobis(4-cyanovaleric acid),4,4′-Azobis(4-cyanovaleric acid)≧75%,1,1′-Azobis(cyclohexanecarbonitrile) 98%, Azobisisobutyronitrile,2,2′-Azobis(2-methylpropionamidine)dihydrochloride,2,2′-Azobis(2-methylpropionitrile), 2,2′-Azobis(2-methylpropionitrile),tert-Butyl hydroperoxide, tert-Butyl peracetate, cumene hydroperoxide,2,5-Di(tert-butylperoxy)-2,5-dimethyl-3-hexyne,2,5-Di(tert-butylperoxy)-2,5-dimethyl-3-hexyne, Dicumyl peroxide,2,5-Bis(tert-butylperoxy)-2,5-dimethylhexane, 2,4-Pentanedione peroxide,1,1-Bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-Bis(tert-butylperoxy)cyclohexane,1,1-Bis(tert-amylperoxy)cyclohexane, Benzoyl peroxide, 2-Butanoneperoxide, tert-Butyl peroxide, Lauroyl peroxide, tert-Butylperoxybenzoate, tert-Butylperoxy 2-ethylhexyl carbonate, tert-Butylhydroperoxide, in an amount of 0.0% to 5.0% by weight of the totalcoating composition.

The photo radical initiators may be selected from the group consistingof Acetophenone, Anisoin, Anthraquinone, Anthraquinone-2-sulfonic acid,sodium salt monohydrate, (Benzene)tricarbonylchromium, Benzil, Benzoin,Benzoin ethyl ether, Benzoin isobutyl ether, Benzoin methyl ether,Benzophenone, Benzophenone/1-Hydroxycyclohexyl phenyl ketone,3,3′,4,4′-Benzophenonetetracarboxylic dianhydride, 4-Benzoylbiphenyl,2-Benzyl-2-(dimethylamino)-4′-morpholinobutyrophenone,4,4′-Bis(diethylamino)benzophenone, 4,4′-Bis(dimethylamino)benzophenone,Camphorquinone, 2-Chlorothioxanthen-9-one,(Cumene)cyclopentadienyliron(II) hexafluorophosphate, Dibenzosuberenone,2,2-Diethoxyacetophenone, 4,4′-Dihydroxybenzophenone,2,2-Dimethoxy-2-phenylacetophenone, 4-(Dimethylamino)benzophenone,4,4′-Dimethylbenzil, 2,5-Dimethylbenzophenone, 3,4-Dimethylbenzophenone,Diphenyl(2,4,6-trimethylbenzoyl)phosphineoxide/2-Hydroxy-2-methylpropiophenone, 4′-Ethoxyacetophenone,2-Ethylanthraquinone, Ferrocene, 3 3′-Hydroxyacetophenone,4′-Hydroxyacetophenone, 3-Hydroxybenzophenone, 4-Hydroxybenzophenone,1-Hydroxycyclohexyl phenyl ketone, 2-Hydroxy-2-methylpropiophenone,2-Methylbenzophenone, 3-Methylbenzophenone, Methybenzoylformate,2-Methyl-4′-(methylthio)-2-morpholinopropiophenone, Phenanthrenequinone,4′-Phenoxyacetophenone, Thioxanthen-9-one, Triarylsulfoniumhexafluoroantimonate salts, Triarylsulfonium hexafluorophosphate salts,in an amount of 0.0% to 5.0% by weight of the total coating composition.

The cross-linker may be selected from the group consisting of glycerol,glyoxal, methylglyoxal, dulcitol, 1,5-pentanediol, 1,3-propanediol,1,2,4-butanetriol, 1,4-butanediol,1,1-bis(trichlorosilylmethyl)ethylene, 1,10-bis(trichlorosilyl)decane,1,10-bis(triethoxysilyl)decane, 1,12-bis(methyldichlorosilyl)ethane,1,2-bis(methyldiethoxysilyl)ethane,1,2-bis(methyldiethoxysilyl)ethylene,1,2-bis(methyldimethoxysilyl)ethane,1,2-bis(methyldimethoxysilyl)ethylene, 1,2-bis(trichlorosilyl)decane,1,2-bis(trichlorosilyl)ethane, 1,2-bis(triethoxysilyl)ethane,1,2-bis(triethoxysilyl)ethylene, 1,4-bis(trimethoxysilyl)benzene,1,4-bis(triethoxysilyl)benzene, 1,4-bis(trichlorosilyl)benzene,1,4-bis(triethoxysilylethyl)benzene,1,4-bis(trichlorosilylethyl)benzene,1,4-bis(trimethoxysilylmethyl)benzene,1,4-bis(triethoxysilylmethyl)benzene,1,4-bis(trichlorosilylmethyl)benzene,1,4-bis(trimethoxysilylpropyl)benzene,1,4-bis(triethoxysilylpropyl)benzene,1,4-bis(trichlorosilylpropyl)benzene in an amount of 0.0% to 5.0% byweight of the total coating composition.

The surfactant may be selected from the group consisting of nonionicsurfactants, polyoxyethylene glycol alkyl ethers (Brij 58),polyoxyethylene octyl phenyl ether, polyoxyethylene glycol sorbitanalkyl esters (polysorbate), ionic surfactants, cetyltrimethylammoniumbromide and other tetraalkylammonium halides in an amount of 0.0% to5.0% by weight of the total coating composition.

In some embodiments other heteroatom containing additive(s) such asboron or aluminum selected from a group consisting of B(OH)₃, BI₃,B(OCH₃)₃, B(OC₂H₅)₃, BCl₃, Al(acac)₃ or AlCl₃ may be added duringsynthesis of the siloxane polymer or during final formulation in anamount of 0% to 1.0% by weight of the total coating composition.

In an aspect, a siloxane polymer solution composition may include (i) asiloxane polymer A formed from acid hydrolyzed alkoxysilanes,organosilane, and organofluorosilane, wherein the siloxane polymer A hasthe following formula:

[RSi(OH)₂O_(0.5)]_(a)[RSiO_(1.5)]_(b)[RSi(OH)O]_(c)[R′Si(OH)₂O_(0.5)]_(m)[R′SiO_(1.5)]_(n)[R′Si(OH)O]_(p)[SiO₂]_(W)[Si(OH)O_(1.5)]_(x)[Si(OH)₂O]_(y)[Si(OH)₃O_(0.5)]_(z),where R is selected from the group consisting of independently methyl oroptionally substituted or unsubstituted C2 to C10 alkyl group, asubstituted or unsubstituted C3 to C20 cycloalkyl group, a substitutedor unsubstituted C1 to C10 hydroxyalkyl group, a substituted orunsubstituted C6 to C20 aryl group, a substituted or unsubstituted C2 toC20 heteroaryl group, a substituted or unsubstituted C2 to C10 alkenylgroup, a substituted or unsubstituted carboxyl group, a substituted orunsubstituted (meth)acryl group a substituted or unsubstitutedglycidylether group, or a combination thereof, R′ is selected from thegroup consisting of a fluorine substituted C3 alkyl group or optionallyC4 to C10 alkyl group, a fluorine substituted C3 to C20 cycloalkylgroup, a fluorine substituted C1 to C10 hydroxyalkyl group, a fluorinesubstituted aryl group, a fluorine substituted C2 to C20 heteroarylgroup, a fluorine substituted C2 to C10 alkenyl group, a fluorinesubstituted carboxyl group, a substituted or unsubstituted (meth)acrylgroup, a fluorine substituted glycidylether group, or a combinationthereof, 0<a,b,c,w,x,y,z<0.9, 0≦m,n,p<0.9, and a+b+c+m+n+p+w+x+y+z=1,(ii) a hydrolysis acid catalyst, (iii) a polar organic solvent, and (iv)at least one additive selected from the group consisting of: a thermalradical initiator, a photo radical initiator and a crosslinker. In someembodiments, the hydrolyzed organosilane and the hydrolyzedorganofluorosilane are each separately prepared before combining witheach other and with alkoxysilane or with another reagent. Someembodiments may also include one or more of a porogen, a template, anano-filler, an adhesion promoter, a Si—OH condensation catalyst and asurfactant.

The siloxane polymer solution may be prepared in a two-step processincluding preparing hydrolyzed organosilane before combining with analkoxysilane, or preparing hydrolyzed alkoxysilane before combining withorganosilane and fluorosilane, or preparing the hydrolyzed alkoxysilanebefore combining with organosilane.

In an aspect, a method of forming a coating on a substrate, such as aglass or other substrate, may include preparing a siloxane polymersolution composition including: a siloxane polymer A formed from acidhydrolyzed alkoxysilanes, organosilane, and organofluorosilane, whereinthe siloxane polymer A has the following formula:

[RSi(OH)₂O_(0.5)]_(a)[RSiO_(1.5)]_(b)[RSi(OH)O]_(c)[R′Si(OH)₂O_(0.5)]_(m)[R′SiO_(1.5)]_(n)[R′Si(OH)O]_(p)[SiO₂]_(W)[Si(OH)O_(1.5)]_(x)[Si(OH)₂O]_(y)[Si(OH)₃O_(0.5)]_(z),where R is selected from the group consisting of independently methyl oroptionally substituted or unsubstituted C2 to C10 alkyl group, asubstituted or unsubstituted C3 to C20 cycloalkyl group, a substitutedor unsubstituted C1 to C10 hydroxyalkyl group, a substituted orunsubstituted C6 to C20 aryl group, a substituted or unsubstituted C2 toC20 heteroaryl group, a substituted or unsubstituted C2 to C10 alkenylgroup, a substituted or unsubstituted carboxyl group, a substituted orunsubstituted (meth)acryl group a substituted or unsubstitutedglycidylether group, or a combination thereof, R′ is selected from thegroup consisting of a fluorine substituted C3 alkyl group or optionallyC4 to C10 alkyl group, a fluorine substituted C3 to C20 cycloalkylgroup, a fluorine substituted C1 to C10 hydroxyalkyl group, a fluorinesubstituted aryl group, a fluorine substituted C2 to C20 heteroarylgroup, a fluorine substituted C2 to C10 alkenyl group, a fluorinesubstituted carboxyl group, a substituted or unsubstituted (meth)acrylgroup, a fluorine substituted glycidylether group, or a combinationthereof, 0<a,b,c,w,x,y,z<0.9, 0≦m,n,p<0.9, and a+b+c+m+n+p+w+x+y+z=1, ahydrolysis acid catalyst, a polar organic solvent, and at least oneadditive selected from the group consisting of: a porogen or template, athermal radical initiator, a photo radical initiator and a crosslinker.The method also includes coating the substrate with the siloxane polymersolution, and curing the coating to form a thin film. Some embodimentsof the coating may also include one or more of a porogen, a template, anano-filler, an adhesion promoter, a Si—OH condensation catalyst and asurfactant. A coated glass substrate may be formed by the method. Insome embodiments, the hydrolyzed organosilane and the hydrolyzedorganofluorosilane are each separately prepared before combining witheach other and with alkoxysilane or with another reagent. The substratemay be coated by solution coating, by roller coating or by anothermethod.

The coating composition of the present invention may be applied to asubstrate by first ensuring the surface is clean and activated such thatit exhibits a high surface energy, for example exhibiting a watercontact angle of less than 60°. Then by applying the coating compositionto the surface by dip-coating, flow-coating, spray-coating,roll-coating, slot-die coating and the like and thereafter allowed it todry to form a dried gel coating on the surface. The coating is thencured by heating to about 120° C. to about 800° C. The coating may bethermally cured at about 120° C. to about 800° C. The coating may bethermally cured at less than about 350° C.

After curing the coating may have a thickness of about 100 nm to about500 nm or between about 60 nm and 150 nm. In aspects, the coating has athickness of about 80 nm to about 500 nm after curing, or 80 nm to about160 nm after curing.

In an aspect, a coating may include a dried gel prepared from: asiloxane polymer A formed from acid hydrolyzed alkoxysilanes,organosilane, and organofluorosilane, wherein the siloxane polymer A hasthe following formula:

[RSi(OH)₂O_(0.5)]_(a)[RSiO_(1.5)]_(b)[RSi(OH)O]_(c)[R′Si(OH)₂O_(0.5)]_(m)[R′SiO_(1.5)]_(n)[R′Si(OH)O]_(p)[SiO₂]_(W)[Si(OH)O_(1.5)]_(x)[Si(OH)₂O]_(y)[Si(OH)₃O_(0.5)]_(z),where R is selected from the group consisting of independently methyl oroptionally substituted or unsubstituted C2 to C10 alkyl group, asubstituted or unsubstituted C3 to C20 cycloalkyl group, a substitutedor unsubstituted C1 to C10 hydroxyalkyl group, a substituted orunsubstituted C6 to C20 aryl group, a substituted or unsubstituted C2 toC20 heteroaryl group, a substituted or unsubstituted C2 to C10 alkenylgroup, a substituted or unsubstituted carboxyl group, a substituted orunsubstituted (meth)acryl group a substituted or unsubstitutedglycidylether group, or a combination thereof, R′ is selected from thegroup consisting of a fluorine substituted C3 alkyl group or optionallyC4 to C10 alkyl group, a fluorine substituted C3 to C20 cycloalkylgroup, a fluorine substituted C1 to C10 hydroxyalkyl group, a fluorinesubstituted aryl group, a fluorine substituted C2 to C20 heteroarylgroup, a fluorine substituted C2 to C10 alkenyl group, a fluorinesubstituted carboxyl group, a substituted or unsubstituted (meth)acrylgroup, a fluorine substituted glycidylether group, or a combinationthereof, 0<a,b,c,w,x,y,z<0.9, 0≦m,n,p<0.9, and a+b+c+m+n+p+w+x+y+z=1, ahydrolysis acid catalyst, a polar organic solvent, and at least oneadditive selected from the group consisting of: a thermal radicalinitiator, a photo radical initiator and a crosslinker. In someembodiments, the coating may also include one or more of a porogen, atemplate, a nano-filler, an adhesion promoter, a Si—OH condensationcatalyst and a surfactant. In some embodiments, the hydrolyzedorganosilane and the hydrolyzed organofluorosilane are each separatelyprepared before combining with each other and with alkoxysilane or withanother reagent,

In an embodiment wherein the coating is applied to a soda-lime glasssubstrate the absolute reflection from the surface may exhibit areduction in reflection of about 1.0% to about 3.5% as compared to anuncoated surface. In some embodiments the coating exhibits excellentabrasion resistance and adhesion to glass, for example the ability topass abrasion testing to standard EN1096-2 with an absolute change inreflection of no more than 0.5% as measured after 1,000 abrasion strokesor even after 2,000 abrasion strokes. In an embodiment wherein thecoating is applied to a solar module, the coating may improve the peakpower output of the solar module by about 1.0% to about 3.5% relative toan uncoated solar module.

In embodiments, the coated substrate may be a window or architecturalglass, or an LED or a semi-conductor or an exposed photovoltaic elementor a lens or a diffuser or a mirror or a windshield or automotive glassor a screen or a display or goggles or eyeglasses or sunglasses orgreenhouse glass or a hybrid solar surface or a marine glass or aviationglass or glass used in transportation or a mobile device screen. In someembodiments, the substrate may be a semiconductor and the coating may beused as a planarization, dielectric or gap-filling layer.

In an aspect, a single layer transparent coating may include ananti-reflective property and a hydrophobic property that is highlyabrasion resistant and, wherein the single layer transparent coatingcontains a plurality of oblate voids and, wherein at least 1% of theoblate voids are open to a surface of the single layer transparentcoating. The thickness of the single layer transparent coating may bebetween 10 nm and 5 μm. A refractive index of the single layertransparent coating may be less than 1.45. An average reflection ofvisible light from a surface of glass coated with the single layertransparent coating may be less than 3%. A T_(AM) of a coated glasssubstrate is at least 1% greater than a T_(AM) of a same type ofuncoated glass substrate. A water contact angle in a test for thehydrophobic property may be greater than 70°. A reduction in opticaltransmission of the single layer transparent coating as measured byT_(AM) after performance of 1000 strokes of abrasion testing accordingto the procedure in standard EN1096.2 may be less than 1.0%. Adistribution of a void diameter of the oblate voids may include aGaussian distribution with a mean of between 10 nm and 150 nm with astandard deviation between 2 nm and 40 nm. A distribution of voiddiameter of the oblate voids may be bi-modal with a first group having aGaussian distribution with a mean between 25 nm and 150 nm and astandard deviation between 5 nm and 40 nm and a second group having aGaussian distribution with a mean between 150 nm and 500 nm and astandard deviation between 25 nm and 50 nm. At least 1% of the oblatevoids may extend through a full thickness of the single layertransparent coating. All of the oblate voids may be contained within afull thickness of the single layer transparent coating. The surface ofthe single layer transparent coating may have a percentage of visiblevoids between 1% and 50%. A porosity of the single layer transparentcoating may be between 50% and 2%. The major axis of the oblate voids inthe single layer transparent coating may be between 5 nm and 500 nm andthe minor axis of the oblate voids is between 3 nm and 150 nm. Theflattening of the oblate voids may be between 0.0 to 0.8. The singlelayer transparent coating may be cured at a temperature of less than400° C. The coating may further include a glass substrate having asurface on which said coating is applied. The coating may furtherinclude a solar module having a surface on which said coating isapplied.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure and the following detailed description of certainembodiments thereof may be understood by reference to the followingfigures:

FIG. 1 a illustrates the UV-vis transmittance spectra comparing thetransmission gains of a coating made from the composition given inExample 2 on tin vs the non-tin side of float glass on a 30×30 cmsubstrate;

FIG. 1 b illustrates the UV-vis transmittance spectra of a coating madefrom Example 3 roll coated on a patterned glass substrate;

FIG. 2 a illustrates the UV-vis transmittance spectra showing maximumtransmittance enhancement of coatings on tin side of TCO glasssubstrates made from compositions given in Example 3 with pre- andpost-abrasion spectra;

FIGS. 2 b and 2 c illustrate the UV-vis spectra of coatings on the tinside of a TCO glass substrate made from composition of example 5 and 7respectively;

FIG. 3 a is TEM cross-sectional view of a coating made from thecomposition of Example 2 on a glass slide substrate;

FIG. 3 b is a High resolution TEM of a coating made from the compositionof Example 2 on a glass substrate;

FIG. 4 is an SEM cross-sectional view of a coating made from thecomposition of Example 2 on a 30×30 cm glass substrate;

FIG. 5 is an SEM cross-sectional view of a coating made from thecomposition of Example 3 on a 30×30 cm glass substrate;

FIG. 6 is an SEM cross-sectional view of a coating made from thecomposition of Example 4 on a 30×30 cm glass substrate;

FIG. 7 a-1 is a GPC of sol made from Example 2;

FIG. 7 a-2 shows the spread of the molecular weights for sols made fromExample 2;

FIG. 7 b-1 is a GPC of sol made from Example 3;

FIG. 7 b-2 shows the spread of the molecular weights for sols made fromExample 3;

FIG. 7 c-1 is a GPC of sol made from Example 4;

FIG. 7 c-2 shows the spread of the molecular weights for sols made fromExample 4;

FIG. 7 d-1 is a GPC of sol made from Example 5;

FIG. 7 d-2 shows the spread of the molecular weights for sols made fromExample 5;

FIG. 7 e-1 is a GPC of sol made from Example 6;

FIG. 7 e-2 shows the spread of the molecular weights for sols made fromExample 6;

FIG. 7 f-1 is a GPC of sol made from Example 7;

FIG. 7 f-2 shows the spread of the molecular weights for sols made fromExample 7;

FIG. 7 g-1 is a GPC of sol made from Example 8;

FIG. 7 g-2 shows the spread of the molecular weights for sols made fromExample 8;

FIG. 7 h-1 is a GPC of sol made from Example 9;

FIG. 7 h-2 shows the spread of the molecular weights for sols made fromExample 9;

FIG. 7 k-1 is a GPC of sol made from Example 10;

FIG. 7 k-2 shows the spread of the molecular weights for sols made fromExample 10;

FIG. 8 a is the XPS spectrum of coating from Example 2 on tin side of TCof TCO coated glass;

FIG. 8 b is the XPS spectrum of coating from Example 2 on tin side ofTCO coated glass after a 10 minute Argon Sputter Etch;

FIG. 9 depicts an embodiment of flow coating;

FIG. 10 depicts a cross-sectional view of an embodiment of a flowcoating head;

FIG. 11 depicts a cross-sectional view of a second embodiment of a flowcoating head;

FIG. 12 depicts an isometric view of a flow coating head lower slotmanifold;

FIG. 13 depicts a partial view of the assembled flow coating head ofFIG. 10 and a corresponding substrate;

FIG. 14 shows a schematic cross-sectional view of a coating slotidentifying several critical dimensions and parameters;

FIGS. 15 a and 15 b depict a roll-coat system optimized for coating onflat substrates;

FIG. 16 depicts an embodiment of a roll-coat system for flat substrates;

FIG. 17 depicts an embodiment of a skin-cure system;

FIG. 18 depicts an example temperature profile for a skin-cure system;

FIG. 19 depicts an example of thermogravimetric analysis ofrepresentative samples of coating material;

FIGS. 20 a, 20 b and 20 c show data for an exemplary sol-gel coatingthat demonstrates control of final film thickness, refractive index andwater contact angle as a function of maximum cure temperature;

FIGS. 20 d and 20 e depict examples of FT-IR analysis of representativesamples of coating material before and after the curing process;

FIGS. 21 and 22 depict Si-NMR spectra of example 2 and 3 respectively;

FIG. 23 is an SEM micrograph of the coated and cured sample of Example19 on float glass;

FIG. 24 is an SEM micrograph of the coated and cured sample of Example11 on rolled glass;

FIG. 25 is an SEM micrograph of the roll-coated and cured sample ofExample 11 on rolled glass;

FIG. 26 is a graph depicting the GPC-based shelf life of sol fromExample 8 at 20° C.;

FIG. 27 is a graph depicting the GPC-based shelf life of sol fromExample 8 at 40° C.;

FIG. 28 and FIG. 29 depict Si-NMR spectra of Examples 33 and 35respectively;

FIG. 30 a depicts a top-down SEM micrograph of the roll-coated and curedsample of Example 55;

FIG. 30 b is a histogram of void diameter derived from the image in FIG.30 a;

FIGS. 31 a, 32 a, 33 a, 34 a, 35 a, and 36 a depict top-down SEMmicrographs of roll-coated and cured samples;

FIGS. 31 b, 32 b, 33 b, 34 b, 35 b, and 36 b are histograms of voiddiameter derived from the images in FIG. 31 a-36 a showing variousdistributions of void size;

FIGS. 37 a-37 d depict an oblique cross-sectional SEM micrographs ofroll-coated and cured samples showing various void structures in thevertical dimension of the coating; and

FIG. 38 illustrates the UV-vis transmittance spectra of coating madefrom Example 55 roll coated on a float-glass substrate.

DETAILED DESCRIPTION

Various embodiments of the disclosure are described below in conjunctionwith the Figures; however, this description should not be viewed aslimiting the scope of the present disclosure. Rather, it should beconsidered as exemplary of various embodiments that fall within thescope of the present disclosure as defined by the claims. Further, itshould also be appreciated that references to “the disclosure” or “thepresent disclosure” should not be construed as meaning that thedescription is directed to only one embodiment or that every embodimentmust contain a given feature described in connection with a particularembodiment or described in connection with the use of such phrases. Infact, various embodiments with common and differing features aredescribed herein.

The present disclosure is generally directed to coatings that provide anoticeable improvement in anti-reflective properties. It is thecombination of the improved anti-reflective properties with theanti-soiling properties, self-cleaning properties and manufacturingflexibility as well as other benefits that further enhances the utilityof the coating. Accordingly, the coatings of the present disclosure maybe used on substrates, such as transparent substrates, to increase thelight transmittance through the substrates. In particular, the coatingsmay be used on transparent substrates such as glass or the front coverglass of solar modules.

Throughout this disclosure, solar modules are used as the exemplaryembodiment, but it should be understood that any optical element may beutilized with the system and methods described herein, such as windows,architectural glass, LEDs, semi-conductors, exposed photovoltaicelements, lenses, diffusers, mirrors, windshields, automotive glass,screens/displays, goggles, eyeglasses, sunglasses, greenhouse glass,hybrid solar surfaces, marine glass, aviation glass, glass used intransportation, mobile device screen, and the like.

The present disclosure is particularly well suited for use with glassused in solar energy generation (“solar glass”). It should be understoodthat solar energy generation includes solar photovoltaic and solarthermal, wherein solar insulation is used to produce heat either as anend-point or as an intermediate step to generate electricity.Furthermore it should be understood that solar glass may be used in anyapplication where maximal transmission of solar energy through the glassis desired such as for example in greenhouses or building environmentswhere warm temperatures are desired. Typically solar glass is hightransmission low iron glass. It may be either float glass, that is, flatglass sheets formed on a molten tin bath or patterned glass wherein theflat glass is formed by the action of rollers. Float glass is oftencharacterized by the presence of tin contamination on the bottom (“tinside”) of the glass. Patterned glass is typically textured on one sideto improve its performance in solar modules. It may also be formed intotubes such as those used as receivers in solar thermal energy generationor in some non-planar forms of solar photovoltaic generation.Embodiments of the present disclosure may also be applied to glasssurfaces used as mirrors in solar energy generation such as parabolictrough systems or in heliostats. It may also be used to coat variousglass lenses such as Fresnel lenses used in solar thermal generation.

Additionally, solar glass may have various coatings applied. For examplea common coating is a transparent conductive oxide (TCO) such asfluorine doped tin oxide (FTO) or indium tin oxide (ITO) on one side ofthe glass. This coating is used to provide the front electrode for manythin film solar module technologies. Other coatings may be present suchas coatings to seal in alkali ions such as Na+ and Ca++ that are used inthe manufacturer of the glass but that cause long term reliabilityproblems when leached out by water. Other techniques to solve thisproblem are to deplete these ions in thin layers of the glass surface.Solar glass may also be coated with a reflective surface to form amirror. Solar glass may be tempered, annealed or un-tempered. Temperedglass is significantly stronger and solar modules manufactured using ittypically only use one sheet of glass. If very thin tempered glass isused, then a second thin sheet of glass may be used as a back sheet forthe solar module. Solar modules manufactured with un-tempered frontglass typically use a back sheet of tempered glass to meet strength andsafety requirements. Many thin-film solar photovoltaic technologies alsouse the front glass as a substrate upon which they deposit materialsthat comprise the solar cell. The processes used during the manufacturerof the solar cell may adversely affect the properties of any existingcoatings on the glass or existing coatings may interfere with the solarcell manufacturing process. Embodiments of the present disclosure arecompletely tolerant of type of glass selected by the solar modulemanufacturer. It works well on float or patterned glass.

One critical issue for solar module manufacturers that use TCO (orsimilar) coated glass is tempering. It is very difficult to achievelow-cost, high quality TCO coated tempered glass. Therefore solar modulemanufacturers that requite TCO coated glass use untempered glass.Additionally, even if suitable TCO coated tempered glass is available,some thin-film solar manufacturing processes heat the glass duringmanufacturer to the extent that the temper is lost. Much of theanti-reflective coated glass on the market is tempered. Tempering is theprocess by which the glass is heated to 600° C. to 700° C., then quicklycooled. This high tempering temperature sinters the anti-reflectivecoating providing it with its final mechanical strength. Thus, solarmodule manufacturers that cannot use tempered glass typically cannot useanti-reflective coated glass. In addition, some module manufacturers,especially thin film module manufacturers who might need to applyanti-reflective coatings on finished or substantially finished modulesare unable to use currently available anti-reflective coatings becausethe coating materials need to be cured at temperatures greater than 300°C., exposed to a corrosive ammonia atmosphere, or exposed to highlytoxic acids like hydrofluoric acid. Exposing finished or substantiallyfinished solar modules to temperatures >300° C. or exposing them to acorrosive ammonia atmosphere is likely to damage their performanceand/or long term reliability. Exposing finished modules to acids orother strong etchants to create a graded refractive index layer isequally challenging and poses an additional safety risk due to managingand disposing large quantities of a highly dangerous chemical likehydrofluoric acid. One of the embodiments of the disclosure may beapplied and cured at a low temperature of between 20° C. and 300° C. andbetween 20° C. and 130° C. and further between 80° C. and 250° C. Thislow temperature facilitates the coating of completed solar panelswithout damage to the panel. Thus, it is an anti-reflective solution forusers of un-tempered solar glass and for users of anti-reflectivecoatings on finished or substantially finished solar modules.

The low temperature curing of one of the embodiments of the disclosurealso provides substantial benefits to solar module manufacturers beyondenabling un-tempered anti-reflective glass. By making possible thecoating of the glass without the need for the tempering step, solarmodule manufacturers are enabled to apply their own anti-reflectivecoating. Currently the requirement for a large tempering oven means thatsolar modules manufacturers are restricted to buying anti-reflectiveglass from glass manufacturers. This means that they must maintaininventory of both anti-reflective coated and non-coated glass. As thesecannot be used interchangeably, inventory flexibility is reduced,necessitating keeping larger amounts of inventory on hand. The abilityfor solar module manufacturers to apply their own coating means thatthey can just hold a smaller inventory of non-coated glass and thenapply the anti-reflective coating to that as needed.

In addition, conventional anti-reflective coatings are prone toscratching during the solar module manufacturing process. Typicallysolar module manufacturers must use a plastic or paper sheet to protectthe coating. As the coatings disclosed herein can be applied to fullymanufactured solar modules, it can be applied at the end of themanufacturing process, thus removing the need for the protection sheetand the opportunity for damage to the coating during manufacture.

Conventional anti-reflective coatings from different manufacturers tendto have subtle color, texture and optical differences. This presentsproblems to solar module manufacturers who desire their products to havea completely consistent cosmetic finish. If they manufacture largenumbers of solar modules it is almost inevitable that they will have toorder anti-reflective glass from different suppliers causing slightdifferences in the appearance of the final products. However, thecoatings disclosed herein enable solar module manufacturers to applytheir own coating and so enables cosmetic consistency over an unlimitednumber of solar modules.

For anti-reflective coatings on solar modules, it is also important totune and optimize the thickness of the antireflective coating on glassdepending upon the type of solar cell that is used by a solar modulemanufacturer. This is because the spectral responses for crystallinesilicon, amorphous silicon, CdTe, CIGS, and other solar cell absorbermaterials have slight differences and it would be beneficial for thethickness of an antireflective coating to be optimized such that themaximum transmission for the antireflective coating occurs atwavelengths that are well matched to that of the underlying solar cellmaterial.

In addition, to their anti-reflective properties, the coatings describedherein can exhibit anti-soiling and/or self-cleaning properties, as theyare resistant to the adhesion of dirt and promote the removal of anyadhered dirt by the action of water. More specifically, some embodimentsof the coatings described herein can be characterized by extremely fineporosity that minimizes the deposition of dirt by physical means.Further, some embodiments of the coatings are characterized by a lowenergy surface that resists chemical and physical interactions and makesit easy to dislodge the particles, thereby making the surfacesessentially anti-soiling. The reduced physical and/or chemicalinteractions with the environment, such as dirt, make the exposedsurface of these coating less susceptible to binding of dirt and alsomake it easier to clean with a minimal expenditure of force or energy.

Typically in order to completely clean ordinary glass a mechanicalaction, for example using brushes or high-pressure jets, is required todislodge dirt that is strongly adhered to the surface. However, someembodiments of the coatings described herein present a surface such thatdirt is more attracted to water than to the surface. Thus, in thepresence of water, any dirt resting on the surface may be efficientlyremoved without the need for mechanical action. This means that coatedglass may achieve a high level of cleanliness in the presence of naturalor artificial rain without human or mechanical intervention. Inaddition, the amount of water required to clean the glass is reduced.This is of special significance given that the most effective locationsfor solar energy generation tend to be sunny, warm and arid, and watermay be a particularly expensive and scarce resource in the verylocations where solar energy is most effective.

Embodiments of the disclosure enable a reduction in the Levelized Costof Energy (LCOE) to the operator of a solar energy generating system.First, the anti-reflective property increases the efficiency of thesolar modules. Increased efficiency enables a reduction of cost in theBalance of System (BOS) costs in construction of the solar energygeneration system. Thus for a given size of system the capital costs andconstruction labor costs are lower. Second, the anti-soiling propertyincreases the energy output of the solar modules by reducing the lossesdue to soiling. Third the Operating and Maintenance (O&M) costs arereduced because fewer or no washings are needed reducing labor and watercost associated with washing.

In some embodiments described herein, the coating may also containwater- and oil-resistant hydro/fluoro-carbon groups that make themchemically less reactive and less interacting. When used in combinationwith a glass substrate, the coatings may bind to the glass surface usingsiloxane linkages that make them adhere strongly and makes them strong,durable, and abrasion and scratch resistant. These coatings may bephysically and chemically less reactive, mechanically and structurallystable, hydrophobic, oleophobic, stable and resistant to degradation bysolar ultra-violet (UV) light. Accordingly, it should be appreciatedthat the coatings described herein have particular application totransparent substrates that are exposed to the environment, such asexterior windows and glass used by solar modules.

Generally, the coatings described herein are prepared by a sol-gelprocess. The coating composition includes a hydrolysate oforganoalkoxysilane or a combination of organoalkoxysilanes andtetraalkoxysilane in a form of a homogenous gel-free solution of sol.This sol can be coated onto a substrate using coating techniques knownin the art, dried to form a gel, and cured to form a hard layer orcoating having the properties noted above. The process of curing thedried gel further densifies the coating.

Generally, the resulting properties of the coating described above areprovided by using a particular combination of components in theformation of the final coating. In particular, the selection of aparticular organosilane precursor or mixture of organosilane precursorsin combination with other components in the coating mixture may beimportant in providing a coating with the desired properties. Inembodiments, the coatings may be made from a mixture of precursorsincluding tetraalkoxysilane, organosilane, and organofluorosilanes. Inembodiments, the coatings may be made from a mixture of precursorsincluding tetraalkoxysilane and organosilane. In some embodiments,separate coating mixtures or mixtures of organosilane precursors may beused to form separate sols that may then be combined to form a final solthat is applied to a substrate to be coated. Further, a single sol, orseparately prepared sols that are combined together, may be combinedwith another organosilane precursor to form a final sol that is appliedto a substrate to be coated.

In an embodiment, acid-catalyzed hydrolysis of tetraalkoxysilane formsan extensively cross-linked structure due to the formation of fourSi—O—Si linkages around each silicon atom. These structures arecharacterized by mechanical stability and abrasion resistance. To imparthydrophobicity and anti-soiling to the ultimate coating,organoalkoxysilane(s) may be used in addition to the tetraalkoxysilane.In embodiments, fluorine-containing organoalkoxysilane(s) may be used toimpart oleophobicity in addition to the tetralkoxysilane.

In some embodiments the siloxane polymer is formed from acid hydrolyzedalkoxysilanes, organosilanes and optionally organofluorosilanes, whereinthe organosilane and the optional organofluorosilanes are eachseparately prepared by hydrolyzing in the presence of a hydrolysis acidcatalyst and a solvent in a first step before combining with analkoxysilane in a second step.

In some embodiments the siloxane polymer is formed by hydrolyzing atleast one organotrialkoxysilane or tetraalkoxysilane in the presence ofacid catalyst in a solvent followed by reacting the resulting highlybranched high silanol containing siloxane polymer with tetraalkoxysilaneor organotrialkoxysilane.

The siloxane polymer may have a relative weight percent ratio oftetraalkoxysilane to a total of organosilane and organofluorosilane ofabout 0.2 to about 2.

The alkoxysilane may be selected from the group consisting oftetramethoxysilane and tetraethoxysilane.

The organosilane may be selected from the group consisting oftrimethoxysilane, triethoxysilane, methyltrimethoxysilane,methyltriethoxysilane, n-propyltrimethoxysilane,n-propyltriethoxysilane, iso-propyltrimethoxysilane,iso-propyltriethoxysilane, n-butyltrimethoxysilane,n-butyltriethoxysilane, iso-butyltrimethoxysilane,iso-butyltriethoxysilane, 3,3-dimethylbutyltrimethoxysilane,3,3-dimethylbutyltriethoxysilane, pentyltrimethoxysilane,pentyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane,heptyltrimethoxysilane, heptyltriethoxysilane, octyltrimethoxysilane,octyltriethoxysilane, n-decyltrimethoxysilane, n-decyltriethoxysilane,dodecyltrimethoxysilane, dodecyltriethoxysilane,cyclopentyltrimethoxysilane, cyclopentyltriethoxysilane,cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane,phenyltrimethoxysilane, phenyltriethoxysilane, vinyltrimethoxysilane,vinyltriethoxysilane, allyltrimethoxysilane, allyltriethoxysilane,acetoxymethyltrimethoxysilane, acetoxymethyltriethoxysilane,acetoxyethyltrimethoxysilane, acetoxyethyltriethoxysilane,(3-acetoxypropyl)trimethoxysilane, (3-acetoxypropyl)triethoxysilane,acryloxymethyltrimethoxysilane, acryloxymethyltriethoxysilane,(3-acryloxypropyl)trimethoxysilane, (3-acryloxypropyl)triethoxysilane,methacryloxymethyltrimethoxysilane, methacryloxymethyltriethoxysilane,(3-methacryloxypropyl)trimethoxysilane,(3-methacryloxypropyl)triethoxysilane,(3-glycidylpropyl)trimethoxysilane, (3-glycidylpropyl)triethoxysilane.

The organofluorosilane can be selected from a group consisting of(3,3,3-trifluoropropyl)triemthoxysilane,(3,3,3-trifluoropropyl)triethoxysilane,dodecyafluorodec-9-ene-1-yltrimethoxysilane,dodecyafluorodec-9-ene-1-yltriethoxysilane,(heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane,(heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane,3-(heptafluoroisopropoxy)propyltrimethoxysilane,3-(heptafluoroisopropoxy)propyltriethoxysilane,hexadecafluorododec-11-en-1-yltrimethoxysilane,hexadecafluorododec-11-en-1-yltriethoxysilane,nonafluorohexyltrimethoxysilane, nonafluorohexyltriethoxysilane,pentafluorophenoxyundecyltrimethoxysilane,pentafluorophenoxyundecyltriethoxysilane,pentafluorophenyltrimethoxysilane, pentafluorophenyltriethoxysilane,(tridecafluoro-1,1,2,2-tetrahydrooctyl)trimethoxysilane,(tridecafluoro-1,1,2,2-tetrahydrooctyl)triethoxysilane,perfluorooctylphenyltrimethoxysilane,perfluorooctylphenyltriethoxysilne,heptadecafluorodecyltrimethoxysilane,heptadecafluorodecyltriethoxysilane,(1H,1H,2H,2H-tridecafluoro-n-octyl)trimethoxysilane,(1H,1H,2H,2H-tridecafluoro-n-octyl)triethoxysilane,(1H,1H,2H,2H-nonafluorohexyl)trimethoxysilane,(1H,1H,2H,2H-nonafluorohexyl)triethoxysilane,3-(pentafluorophenyl)propyltrimethoxysilane,3-(pentafluorophenyl)propyltriethoxysilane.

The siloxane polymer may be 0.1% to 10% by weight of the total coatingcomposition. The siloxane polymer may have a weight average molecularweight (Mw) of 600 to 10,000 Daltons. The siloxane polymer may include10 to 60 mol % Si—OH groups as established by Si-NMR.

The hydrolysis acid catalyst may be selected from the group consistingof hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid,methanesulfonic acid or acetic acid in amount of 0.01% to 1.0% by weightof the total coating composition.

The solvent may consist of water and at least one other organic solventselected from the group consisting of alcohols, esters, ethers,aldehydes, and ketones such as methanol, ethanol, 1-propanol,2-propanol, 1-butanol, ethyl acetate, ethylene glycol, foramide,dimethylformamide, N-methylpyrrolidinone, propylene glycol methyl ether,1-methoxy-2-propanol, propylene glycol, propylene glycolmethyletheracetate, acetone, cyclohexanone, methylethylkeone,N,N-dimethyl acetamide, dimethylether, diethylether, 2-butanol,2-butanone, tetrahydrofurane, 1,2-diethoxyethane, diethyleneglycol, 1,2dimethoxyethane, dipropylene glycol monomethyl ether acetate, propyleneglycol, diamyl ether, diethyl oxalate, lactic acid butyl ester, dibutylether, 1-pentanol, dimethoxy ethane, 1-hexanol, 1-heptanol, ethyleneglycol, gamma-butyrolactone, triethylene glycol and methyl t-butylether, wherein the amount of solvent is from about 50% to about 99.5% byweight of the total coating composition.

In embodiments, the ratio of organic solvent to water may be betweenabout 1 to about 50 or between about 5 to about 10.

In some embodiments, additives such as high-boiling-point porogens,templates, nano-fillers, adhesion promoters, base condensationcatalysts, thermal radical initiators, photo radical initiators,cross-linkers and surfactants and others may be used in the coatingcomposition.

In some embodiments, a combination of organoalkoxysilane andtetraalkoxysilane precursors with nano-fillers such as colloidal silica(NALCO, NISSAN, EVONIK, LUDOX, BAXTER, CLARIANT), hollow silicanano-spheres, polymer beads, polylactic acid, polyvinylpyrrolidone,polymethylmethactrylates and polyacrylates, carbon nanotubes,Buckminsterfullerene C₆₀ and C₇₀ in an amount of 0.0% to 5% by weight ofthe total coating composition could provide a sol with a longshelf-life, and superior optical and mechanical performance.

In some embodiments, high-boiling-point porogen(s) selected from thegroup consisting of ethylene oxide, propylene oxide, polyethyleneoxides, polypropylene oxides, ethylene oxide/propylene oxide blockco-polymers, polyoxyethylated polyoxypropylated glycols, fatty acidethoxylates, ethylene glycol esters, glycerol esters,mono-di-glycerides, glycerylesters, polyethylene glycolesters,polyglycerol esters, polyglyceryl esters, polyol monoesters,polypropylene glycol esters, polyoxyalkylene glycol esters,polyoxyalkylene propylene glycol esters, polyoxyalkylene polyol esters,polyoxyalkylene glyceride esters, polyoxyalkylene fatty acid, sorbitanesters, sorbitan fatty acid esters, sorbitan esters, polyoxyalkylenesorbitan esters, polyoxyethylene sorbitan monolaurate, polyoxyethylenesorbitan monostearate, polyoxyethylene sorbitan tristearate, sorbitanester ethoxylates such as TWEEN 80, TWEEN 20, PEG 600, PEG 400, PEG 300,or PEG-b-PPG-b-PEG may be added in the amount of 0.0% to 5% by weight ofthe total coating composition to generate porosity in the final filmsthat results in lowering refractive index (RI) and increasing opticalperformance. After gelation of the coating, the high-boiling-pointporogen may remain homogenously dispersed in the gel. During thermalcuring, the gel forms a stronger network of crosslinked Si—O—Si bondingaround high-boiling-point porogens. The network structure may be hardenough to keep its shape at higher temperature when the porogensevaporate or burn off. The loss of porogens may result in pores or voidswhich reduce the refractive index of the coating.

In some embodiments, a stable sol may be synthesized with initialtemplate(s) selected from the group consisting of ethylene oxide,propylene oxide, polyethylene oxides, polypropylene oxides, ethyleneoxide/propylene oxide block co-polymers, polyoxyethylatedpolyoxypropylated glycols, fatty acid ethoxylates, ethylene glycolesters, glycerol esters, mono-di-glycerides, glycerylesters,polyethylene glycolesters, polyglycerol esters, polyglyceryl esters,polyol monoesters, polypropylene glycol esters, polyoxyalkylene glycolesters, polyoxyalkylene propylene glycol esters, polyoxyalkylene polyolesters, polyoxyalkylene glyceride esters, polyoxyalkylene fatty acid,sorbitan esters, sorbitan fatty acid esters, sorbitan esters,polyoxyalkylene sorbitan esters, polyoxyethylene sorbitan monolaurate,polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitantristearate, sorbitan ester ethoxylates such as TWEEN 80, TWEEN 20, PEG600, PEG 400, PEG 300, or PEG-b-PPG-b-PEG in an amount of 5% by weightof the total coating composition. Coating and curing of the sol fromthis method produces high performance anti-reflective coatings.

In some embodiments, surfactant(s) may be selected from the groupconsisting of nonionic surfactants, polyoxyethylene glycol alkyl ethers(Brij 58), polyoxyethylene octyl phenyl ether, polyoxyethylene glycolsorbitan alkyl esters (polysorbate), ionic surfactants,cetyltrimethylammonium bromide and other tetraalkylammonium halides maybe added to the formulation in an amount of 0.0% to 5.0% by weight oftotal coating composition.

To enhance silanol condensation, increase cross-link density and lowercure temperature, a base condensation catalyst selected from the groupconsisting of alkali metal hydroxide, amide, amines, imidazolines, suchas; potassium hydroxide (KOH), sodium hydroxide (NaOH), cesium hydroxide(CsOH), ammonium hydroxide (NH₄OH), tetramethyl ammonium hydroxide(TMAH), formamide (FA), dimethylformamide (DMF), N-methylpyrrolidinone(NMP), N,N-dimethyl acetamide (DMA), thermal base generator (TBG) ortetramethoxymethyl glycoluril (PowderLink 1174) may be added in anamount of 0.0% to 1.0% by weight of the total coating composition.

In some embodiments, adhesion promoter(s) suitable for the disclosedcompositions may be selected from the group consisting of organosilanecompounds such as (meth)acryloxypropyl trimethoxysilane,(meth)acryloxypropyl triethoxysilane, (meth)acryloxypropyldimethylmethoxysilane, (meth)acryloxypropyl methyldimethoxysilane,3-glycidylpropyl trimethoxysilane, 3-glycidylpropyl triethoxysilane,3-glycidylpropyl dimethylmethoxysilane, 3-glycidylpropylmethyldimethoxysilane and may be used in the amount of 0.0% to 5.0% byweight of the total coating composition.

In some embodiments, the composition may include a thermal radicalinitiator(s) selected from the group consisting of azo-compounds andperoxides. These compounds include 4,4′-Azobis(4-cyanovaleric acid),4,4′-Azobis(4-cyanovaleric acid)≧75%,1,1′-Azobis(cyclohexanecarbonitrile) 98%, Azobisisobutyronitrile,2,2′-Azobis(2-methylpropionamidine)dihydrochloride,2,2′-Azobis(2-methylpropionitrile), 2,2′-Azobis(2-methylpropionitrile),tert-Butyl hydroperoxide, tert-Butyl peracetate, cumene hydroperoxide,2,5-Di(tert-butylperoxy)-2,5-dimethyl-3-hexyne,2,5-Di(tert-butylperoxy)-2,5-dimethyl-3-hexyne, Dicumyl peroxide,2,5-Bis(tert-butylperoxy)-2,5-dimethylhexane, 2,4-Pentanedione peroxide,1,1-Bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-Bis(tert-butylperoxy)cyclohexane,1,1-Bis(tert-amylperoxy)cyclohexane, Benzoyl peroxide, 2-Butanoneperoxide, tert-Butyl peroxide, Lauroyl peroxide, tert-Butylperoxybenzoate, tert-Butylperoxy 2-ethylhexyl carbonate, tert-Butylhydroperoxide may be added to the formulation in an amount of 0.0% to5.0% by weight of the total coating composition.

In some embodiments, the composition may include a photo radicalinitiator(s) selected from the group consisting of Acetophenone,Anisoin, Anthraquinone, Anthraquinone-2-sulfonic acid, sodium saltmonohydrate, (Benzene)tricarbonylchromium, Benzil, Benzoin, Benzoinethyl ether, Benzoin isobutyl ether, Benzoin methyl ether, Benzophenone,Benzophenone/l-Hydroxycyclohexyl phenyl ketone,3,3′,4,4′-Benzophenonetetracarboxylic dianhydride, 4-Benzoylbiphenyl,2-Benzyl-2-(dimethylamino)-4′-morpholinobutyrophenone,4,4′-Bis(diethylamino)benzophenone, 4,4′-Bis(dimethylamino)benzophenone,Camphorquinone, 2-Chlorothioxanthen-9-one,(Cumene)cyclopentadienyliron(II) hexafluorophosphate, Dibenzosuberenone,2,2-Diethoxyacetophenone, 4,4′-Dihydroxybenzophenone,2,2-Dimethoxy-2-phenylacetophenone, 4-(Dimethylamino)benzophenone,4,4′-Dimethylbenzil, 2,5-Dimethylbenzophenone, 3,4-Dimethylbenzophenone,Diphenyl(2,4,6-trimethylbenzoyl)phosphineoxide/2-Hydroxy-2-methylpropiophenone, 4′-Ethoxyacetophenone,2-Ethylanthraquinone, Ferrocene, 3 3′-Hydroxyacetophenone,4′-Hydroxyacetophenone, 3-Hydroxybenzophenone, 4-Hydroxybenzophenone,1-Hydroxycyclohexyl phenyl ketone, 2-Hydroxy-2-methylpropiophenone,2-Methylbenzophenone, 3-Methylbenzophenone, Methybenzoylformate,2-Methyl-4′-(methylthio)-2-morpholinopropiophenone, Phenanthrenequinone,4′-Phenoxyacetophenone, Thioxanthen-9-one, Triarylsulfoniumhexafluoroantimonate salts, Triarylsulfonium hexafluorophosphate saltsmay be added to the formulation in an amount of 0.0% to 5.0% by weightof the total coating composition.

In some embodiments, the composition may include a cross-linker(s)selected from the group consisting of glycerol, glyoxal, methylglyoxal,dulcitol, 1,5-pentanediol, 1,3-propanediol, 1,2,4-butanetriol,1,4-butanediol, 1,1-bis(trichlorosilylmethyl)ethylene,1,10-bis(trichlorosilyl)decane, 1,10-bis(triethoxysilyl)decane,1,12-bis(methyldichlorosilyl)ethane, 1,2-bis(methyldiethoxysilyl)ethane,1,2-bis(methyldiethoxysilyl)ethylene,1,2-bis(methyldimethoxysilyl)ethane,1,2-bis(methyldimethoxysilyl)ethylene, 1,2-bis(trichlorosilyl)decane,1,2-bis(trichlorosilyl)ethane, 1,2-bis(triethoxysilyl)ethane,1,2-bis(triethoxysilyl)ethylene, 1,4-bis(trimethoxysilyl)benzene,1,4-bis(triethoxysilyl)benzene, 1,4-bis(trichlorosilyl)benzene,1,4-bis(triethoxysilylethyl)benzene,1,4-bis(trichlorosilylethyl)benzene,1,4-bis(trimethoxysilylmethyl)benzene,1,4-bis(triethoxysilylmethyl)benzene,1,4-bis(trichlorosilylmethyl)benzene,1,4-bis(trimethoxysilylpropyl)benzene,1,4-bis(triethoxysilylpropyl)benzene,1,4-bis(trichlorosilylpropyl)benzene may be added in an amount of 0.0%to 5.0% by weight of the total coating composition.

In some embodiments, to enhance silanol condensation and increasedensification of the film, other heteroatom containing additive(s) suchas boron or aluminum selected from the group consisting of B(OH)₃, BI₃,B(OCH₃)₃, B(OC₂H₅)₃, BCl₃, Al(acac)₃ or AlCl₃ may be added duringsynthesis of the siloxane polymer or during final formulation in anamount of 0% to 1.0% by weight of the total coating composition.

It should be appreciated that the coating material and process by whichit is applied to the substrate can comprise a larger coating system. Thecoating material may be optimized for a particular coating method andvice versa. Thus, the optimized coating process may be performed by atool optimized to ensure consistency and quality. Therefore, this toolcoupled with the coating materials may comprise the coating system.Given that the benefits of the current disclosure are particularly wellsuited to solar module manufacturers, who may not themselves manufacturetools, it may be desirable to offer a complete solution consisting ofthe coating material, the coating process knowledge and the associatedcoating tool. In the following paragraphs describing the coatingprocess, it should be appreciated that these steps could be executedmanually, automatically using a coating tool or in any combination ofboth. It should also be appreciated that there are several possiblecoating systems wherein different coating materials, coating processesand coating tools are used in combination.

The tool may be a large stand-alone unit intended for operation in afactory setting; it could be a sub-tool, such that it comprises aprocess module that performs the coating process but that is integratedinto another machine that performs other steps in the larger solarmodule manufacturing process. For example, it could be a module attachedto an existing glass washing machine or a module attached to a solarmodule assembly machine. Alternatively, the tool could be portable orsemi-portable, for example mounted on a truck or inside a tractortrailer such that it could be transported to a worksite and used to coatsolar modules during the construction of a large solar installation.Alternatively, it could be designed such that the coating could beapplied to installed solar modules in situ.

In general, three steps may be used to apply the sol to a givensubstrate. First, the substrate is cleaned and pretreated. Second, thesubstrate is coated with the sol or mixture of sols. Third, the finalcoating is formed on the substrate. It should be understood thatadditional or fewer steps may be used to apply the sol.

As an initial step, the substrate is pretreated or pre-cleaned to removesurface impurities and to activate the surface by generating a freshsurface or new binding sites on the surface.

It is desirable to increase the surface energy of the substrate throughpretreatment or cleaning of the substrate surface to form an “activated”surface. For example an activated surface may be one with many exposedSi—OH moieties. An activated surface reduces the contact angle the soland enables effective wetting of the sol on the surface. In someembodiments, a combination of physical polishing or cleaning and/orchemical etching is sufficient to provide even wetting of the sol. Incases, where the surface tension would need to be further lowered, thesubstrate, such as glass, may be pretreated with a dilute surfactantsolution (low molecular weight surfactants such as surfynol, long chainalcohols such as hexanol or octanol, low molecular weight ethylene oxideor propylene oxide, or a commercial dishwasher detergent such asCASCADE®, FINISH®, or ELECTRASOL® to further help the sol spread betteron the glass surface.

Accordingly, surface pretreatment can involve a combination of chemicaland physical treatment of the surface. The chemical treatment steps caninclude (1) cleaning the surface with a solvent or combination ofsolvents, detergents, mild bases like sodium carbonate or ammoniumcarbonate and/or (2) cleaning the surface with a solvent along with anabrasive pad, (3) optionally chemically etching the surface, and/or (4)washing the surface with water. The physical treatment steps can include(1) cleaning the surface with a solvent or combination of solvents, (2)cleaning the surface with a solvent along with particulate abrasives,and (3) washing the surface with water. It should be appreciated that asubstrate can be pretreated by using only the chemical treatment stepsor only the physical treatment steps. Alternatively, both chemical andphysical treatment steps could be used in any combination. It should befurther appreciated that the physical cleaning action of frictionbetween a cleaning brush or pad and the surface is an important aspectof the surface preparation.

In the first chemical treatment step, the surface is treated with asolvent or combination of solvents with variable hydrophobicity. Typicalsolvents used are water, ethanol, isopropanol, acetone, and methyl ethylketone. A commercial glass cleaner (e.g., WINDEX®) can also be employedfor this purposes. The surface may be treated with an individual solventseparately or by using a mixture of solvents. In the second step, anabrasive pad (e.g., SCOTCHBRITE®) is rubbed over the surface with theuse of a solvent, noting that this may be performed in conjunction withthe first step or separately after the first step. In the last step, thesurface is washed or rinsed with water.

One example of substrate preparation by this method involves cleaningthe surface with an organic solvent such as ethanol, isopropanol, oracetone to remove organic surface impurities, dirt, dust, and/or grease(with or without an abrasive pad) followed by cleaning the surface withwater. Another example involves cleaning the surface with methyl ethylketone (with or without an abrasive pad) followed by washing the surfacewith water. Another example is based on using a 1:1 mixture of ethanoland acetone to remove organic impurities followed by washing the surfacewith water.

In some instances an additional, optional step may be included,chemically etching the surface by means of concentrated nitric acid,sulfuric acid, or piranha solution (1:1 mixture of 96% sulfuric acid and30% H₂O₂) may be necessary to make the surface suitable for bonding tothe deposited sol. Typically this step would be performed prior to thelast step of rinsing the surface with water. In one embodiment, thesubstrate may be placed in piranha solution for 20 minutes followed bysoaking in deionized water for 5 minutes. The substrate may then betransferred to another container holding fresh deionized water andsoaked for another 5 minutes. Finally, the substrate is rinsed withdeionized water and air-dried.

The substrate may alternatively or additionally prepared by physicaltreatment. In the physical treatment case, for one embodiment thesurface is simply cleaned with a solvent and the mechanical action of acleaning brush or pad, optionally a surfactant or detergent can be addedto the solvent, after which the substrate is rinsed with water and airdried. In another embodiment the surface is first cleaned with waterfollowed by addition of powdered abrasive particles such as ceria,titania, zirconia, alumina, aluminum silicate, silica, magnesiumhydroxide, aluminum hydroxide particles, silicon carbide, orcombinations thereof onto the surface of the substrate to form a slurryor paste on the surface. The abrasive media can be in the form a powderor it can be in the form of slurry, dispersion, suspension, emulsion, orpaste. The particle size of the abrasives can vary from 0.1 to 10microns and in some embodiments from 1 to 5 microns. The substrate maybe polished with the abrasive slurry via rubbing with a pad (e.g., aSCOTCHBRITE® pad), a cloth, a foam, or paper pad. Alternatively, thesubstrate may be polished by placement on the rotating disc of apolisher followed by application of abrasive slurry on the surface andrubbing with a pad as the substrate rotates on the disc. Anotheralternative method involves use of an electric polisher that can be usedas a rubbing pad in combination with abrasive slurry to polish thesurface. The substrates polished with the slurry are cleaned by waterand air-dried.

After pretreating the surface, the coating is deposited on a substrateby techniques known in the art, including dip coating, spray, droprolling, flow coating or roll coating to form a uniform coating on thesubstrate. Other methods for deposition that can be used includespin-coating; aerosol deposition; ultrasound, heat, or electricaldeposition means; micro-deposition techniques such as ink-jet, spay-jet,xerography; or commercial printing techniques such as silk printing, dotmatrix printing, etc. Deposition of the sol is may be done under ambientconditions or under controlled temperature and humidity conditions. Insome embodiments the temperature is controlled between 20° C. and 35° C.and/or the relative humidity is controlled between 20% and 60% or morepreferably between 25% and 35%.

In some embodiments, the method of deposition is performed via the droprolling method on small surfaces wherein the sol composition is placedonto the surface of a substrate followed by tilting the substrate toenable the liquid to roll across the entire surface. For largersurfaces, the sol may be deposited by flow coating wherein the sol isdispensed from a single nozzle onto a moving substrate at a rate suchthat the flowing sol leads to a uniform deposition onto a surface orfrom multiple nozzles onto a stationary surface or from a slot onto astationary surface. Flow coating is described in greater detailelsewhere herein. Another method of deposition is via depositing theliquid sol onto a substrate followed by use of a mechanical dispersantto spread the liquid evenly onto a substrate. For example, a squeegee orother mechanical device having a sharp, well-defined, uniform edge maybe used to spread the sol such as roll coating which is described ingreater detail herein.

Several variations for depositing the final sol exist. In someembodiments, the final sol is simply deposited on the substrate in onelayer. In some embodiments, a single sol or multiple sols may bedeposited to form multiple layers, thereby forming a multilayeredcoating. In an embodiment, a coating of a sol containing high-silanolterminal groups can be formed as an underlayer for better adhesion to aglass substrate followed by a topcoat of a tetraalkoxysilane to obtainbetter abrasion resistance for the outer surface. In an embodiment, anunderlayer of an organosilane may be deposited followed by thedeposition of a topcoat of a mixture of an organofluoroalkoxysilane anda tetraalkoxysilane. In an embodiment, an underlayer of atetraalkoxysilane may be deposited followed by the deposition of a toplayer using a sol mixture of an organoalkoxysilane and anorganofluoroalkoxysilane. In an embodiment, an underlayer of a sol madefrom a mixture of an organoalkoxysilane and an organofluoroalkoxysilanemay be deposited followed by vapor deposition of a top layer by exposingthe layer to vapors of a tetraalkoxysilane. In an embodiment, anunderlayer of a sol made from a mixture of an organoalkoxysilane and anorganofluoroalkoxysilane may be deposited followed by deposition of atop layer by immersing the substrate in a solution of atetraalkoxysilane in isopropanol.

In embodiments in which multiple layers are deposited, each layer may bedeposited shortly after deposition of the first layer, for example,within or after 30 seconds of deposition of the prior layer. Inembodiments, sols may be deposited on top of one another, or differentmixtures of sols may be deposited on top of one another or a single solmay be deposited in multiple layers or the same sol mixture may bedeposited in multiple layers. In embodiments, a given sol may bedeposited as one layer and a different sol mixture may be used asanother layers. Any combination of sols may be deposited in any order,thereby constructing a variety of multi-layered coatings.

The sols for each layer may be deposited using either similar ordifferent coating techniques. The coating and curing process steps maybe configured to create coatings of varying complexity and structure. Inembodiments, any combination of coating technique and curing techniquemay be used to achieve a final coating for a substrate. Embodiments mayinclude coating via a flow coating technique followed by a skin cureprocess or cure by conventional means, coating via a spin coatingtechnique followed by a skin cure process or cure by conventional means,coating via a roll coating technique followed by a skin cure process orcure by conventional means, and the like. To generate multilayercoatings, any combination of coating and curing apparatus may be usedsequentially to generate such a coating. The sequential use of suchapparatus may be enabled by an arrangement that places multiple coatingapparatus and curing apparatus in sequence. Alternatively, handlingfacilities may exist for handling the substrate between one or morecoating and curing apparatus. For example, two roll-coaters may beplaced in sequence with an optional flash-off heater in between. Thisfacilitates coating of a first layer by the first roll-coater, drying ofthe layer by the flash-off station, then deposition of a second layer bythe second roll-coater before curing in a skin-cure station or in asimple oven. Alternatively, a high temperature skin-cure step may beinterposed between the roll-coaters to enable a high temperature heattreatment to the first layer before application of the second layer. Itshould be understood that this technique for multiple layer coatings maybe extended to more than two layers. Multi-layer coatings manufacturedby this technique may be high performance anti-reflective interferencetype coatings or multiple layers coatings could be used to modify thesurface energy of the top surface coating by for example adding afluorinated silane mono-layer to an underlying layer to make the finalcoating hydrophobic and oleophobic on the environmentally exposedsurface. The multi-layer coatings may be used to enhance single layeranti-reflective coatings by adding a lower refractive index material onthe environmentally exposed surface to create a graded index coatingbetween the environment and the underlying substrate. In embodiments, asecond layer of coating may be applied to an existing base layer toprovide a functional benefit of the multi-layer coating in combinationwith the base layer. For example, a mobile phone/touch screen glass maybe coated with an inorganic coating that provides anti-scratch benefits,then a low-temperature anti-soiling coating may be on top of theanti-scratch coating.

The thickness of the coatings deposited can vary from about 10 nm toabout 5 μm. In some embodiments, the thickness of the coating variesfrom about 100 nm to about 1 micron, and in other embodiments it variesfrom about 100 nm to about 500 nm. In order to provide sufficientanti-reflective properties, a thickness of about 60 nm to about 150 nmis desired. The thickness of the coating mixture as deposited isaffected by the coating method, as well as by the viscosity of thecoating mixture. Accordingly, the coating method should be selected sothat the desired coating thickness is achieved for any given coatingmixture. Further, in those embodiments, in which multiple layers of solsare deposited, each layer should be deposited in a thickness such thatthe total thickness of the coating is appropriate to achieve the finaldesired transmission spectrum properties. Accordingly, in someembodiments in which multiple layers of sols are deposited, the overallcoating thickness varies from about 100 nm to about 500 nm, and in orderto provide sufficient anti-reflective properties, a total coatingthickness of about 60 nm to about 150 nm is desired.

Once the final sol is deposited as described above, the deposited solwill dry to form a gel through the process of gelation after which thegel is cured further to remove residual solvent and facilitate furthercondensation of Si—OH and network formation via Si—O—Si linkageformation in the coating. In addition, the gel may be allowed to age toallow for the formation of additional linkages throughcontinued-condensation reactions.

As described above, the sol-gel method used in preparing the coatingsdescribed herein utilizes a suitable molecular precursor that is acidhydrolyzed to generate a siloxane oligomers. Initial hydrolysis andpartial condensation of the precursor monomers generates a liquid sol,which ultimately turns to a solid gel during drying. Drying of the gelsunder ambient conditions (or at elevated temperature) leads toevaporation of the solvent phase to form a cross-linked film.Accordingly, throughout the process, the coatingmixture/sol/gel/dried/cured coating undergoes changes in physical,chemical, and structural parameters that intrinsically alter thematerial properties of the final coating. In general, the changesthroughout the sol-gel transformation can be loosely divided into threeinterdependent aspects of physical, chemical, and structural changesthat result in altered structural composition, morphology, andmicrostructure. The chemical composition, physical state, and overallmolecular structure of the sol and the gel are significantly differentsuch that the materials in the two states are intrinsically distinct.

Regarding physical differences, the sol is a collection ofsilanol-containing polysilsesquioxane oligomers (low Mw polymer)dissolved in a polar solvent. These silanol-containingpolysilsesquioxane oligomers are dissolved in a solvent and do notinteract with each other significantly. As such, the sol is stable andexists as a low viscosity transparent colorless liquid. In contrast, ina gel film the network formation has occurred to an advanced state suchthe siloxane polymers are interconnected to each other. The increasednetwork formation and cross-linking makes the gel network rigid with acharacteristic solid state. The ability of the material to exist in twodifferent states is because of the chemical changes (condensation ofSi—OH) that occur along the sol to gel transformation.

Regarding chemical changes, during the sol to gel transition, the solmolecules combine with each other via Si—OH condensation and formationof Si—O—Si linkages. As a result, the material exhibits networkformation and strengthening. Overall, the sol contain reactive Si—OHsilanol groups that can participate in formation of an Si—O—Si networkwhile the gel structure has some of these Si—OH silanol groups convertedinto Si—O—Si groups.

Regarding structural differences, the sol contains few Si—O—Si linkagesalong with terminal Si—OH silanol as well as unhydrolyzed alkoxyligands. As such, the sol state can be considered structurally differentfrom the solidified films, which contain more Si—O—Si linkages and fewersilanols. As such, the liquid sol and the solid state polymeric networksare chemically and structurally distinct systems.

Some combination of organoalkoxysilane precursors could provide a solwith a long shelf-life, while some combination of organoalkoxysilaneprecursors could provide a sol that could gel into a coating withsuperior abrasion resistance, while some other combination oforganoalkoxysilane precursors could gel into a coating with abrasionresistance and anti-soiling properties.

Regarding differences in properties, the origin of the physical andchemical properties of the sol and gel films depends upon theirstructure. The sol solution and the gel films differ in the chemicalcomposition, makeup and functional groups and as a result exhibitdifferent physical and chemical properties. The sol stage because of itsparticulate nature is characterized by high reactivity to form thenetwork while the gel state is largely unreactive due to conversion ofreactive Si—OH silanol groups to stable Si—O—Si linkages. Accordingly,it is the particular combination of organoalkoxysilane precursors andother chemicals added to the coating mixture that is hydrolyzed andcondensed, gelled, dried and cured on a substrate surface that gives thefinal coatings of the present disclosure the desired propertiesdescribed above.

There are several methods by which the gel is dried and cured and/oraged to form the final coating. In some embodiments the gel is dried andcured under ambient or room temperature conditions. In some embodiments,the gel is aged under ambient conditions for 30 minutes followed bydrying for 3 hours in an oven kept at a variable relative humidity of(e.g., 20% to 50%). The temperature of the oven is then increased slowlyat a rate of 5° C./min to a final temperature of 120° C. The slowheating rate along with the moisture slows the rate of the silanolcondensation reaction to provide a more uniform and mechanically stablecoating. This method provides reproducible results and is a reliablemethod of making the coating with the desired properties.

In another embodiment, the gel on the substrate is heated under aninfrared emitter or array of infrared emitters. These emitters areplaced close proximity to the substrate's coated surface such that thesurface is evenly illuminated. The emitters are chosen for maximumemission in the mid-infrared region of 3-5 μm wavelength. This region isdesirable because it is adsorbed better by glass than shorter infraredwavelengths. The power output of the emitters may be closely controlledvia a closed loop PID controller to achieve a precise and controllabletemperature profile of the coated surface. In some embodiments thisprofile will start from ambient temperature and quickly rise 1° C. to100° C. per second to a temperature of 120° C. or to a temperature of275° C. or to 350° C., hold that temperature for a period of 30 to 300seconds, then reduce temperature back to ambient, with or without theaid of cooling airflow.

For applications requiring high throughput and/or for applicationswherein there is a process sensitivity around the maximum allowabletemperature for the bottom surface of the coated glass when the glass iscured it would be preferred to cure the glass such that only the topsurface of the glass is heated by impinging hot air on the coatedsurface or a xenon arc lamp using a pulsing method where the lamp isturned on and off multiple times during the cure cycle. One curingtechnique known as skin curing is described in greater detail elsewhereherein with reference to FIG. 17.

It is particularly noteworthy that some coatings of this disclosure maybe prepared under temperatures not exceeding 120° C. in contrast totemperatures of 400° C. to 600° C. typically employed in curingsilica-based anti-reflective coatings.

In another embodiment, the coating may be dried under ambient or roomtemperature conditions at variable relative humidity of (e.g., 20% to50%). Finally, the coating may be cured at a temperature selected from120° C. to 800° C. for periods of 0.5 min to 60 min.

In another embodiment, the coating may be dried under ambient or roomtemperature conditions at variable relative humidity of (e.g., 20% to50%). Then the coating is cured at tempering conditions.

As described above and as illustrated further in the examples, thecoatings made as described herein have several desirable properties. Thecoatings have anti-reflective properties that reduce the reflection ofphotons. The transmittance of a glass substrate coated with a coatingcomposition made according to the present disclosure can be increased byabout 1% to about 8%, from about 2% to about 6%, and from about 1% toabout 4% relative to uncoated glass substrates

The coatings also have anti-soiling properties, which are also importantin maintaining sufficient transmittance when used in conjunction with aglass substrate. Soiling is due to adherence of particulate matter onsurfaces exposed to environment. The deposition of the particles ontosurfaces depends upon the surface microstructure as well as chemicalcomposition. In general, rough surfaces can provide many sites forphysical binding of particulate matter.

The chemical composition of the surfaces is reflected in the surfaceenergy as measured by contact angles. Low energy surfaces (characterizedby high water contact angles) are usually less susceptible to binding ascompared to high energy surfaces with low water contact angles.Therefore, anti-soiling properties can be determined indirectly bymeasuring the coating's contact angle. The coatings herein providecontact angles ranging from about 10° to about 178°, or about 70° toabout 110° or about 110° to about 155°, or about 125° to about 175°. Thecoatings of this disclosure minimize the photon flux losses due tosoiling by about 50% relative to uncoated samples.

The coatings of the present disclosure also provide desirable abrasionresistance. Abrasion resistance can be defined as the ability of amaterial to withstand erosion due to frictional forces to preserve andmaintain its original shape and appearance. Abrasion resistance relatesto the strength of the intrinsic framework structure as well as tosurface features. Materials that do not have sufficient strength due tolack of long range bonding interactions tend to abrade easily.Similarly, materials with uneven surfaces or coatings with surfaceinhomogeneities and asperities tend to wear due to frictional losses.Also, the leveling and smoothing of these asperities due to frictionleads to changes in optical transmission of the coating as the materialis abraded.

It is possible that the beneficial properties of the coating can also betuned by changing the molecular weight of the sols that comprise thecoating or changing the ratio of low and high molecular weightcomponents in the sols that comprise the coating or by the changing thepolydispersity of the sols that comprise the coating. Altering the pHand changing the catalysts used in the reaction could also be used tochange the molecular weights and molecular weight distribution orpolydispersity of the components in the sol. For example, changing thepolydispersity of the sols could impact how the polymerized silanemolecules pack together. This could have an impact on abrasionresistance of the cured coating. Another example is modifying thesurface characteristics of the final coating by the presence of lowmolecular weight hydrolyzed organofluoroalkoxysilane molecules in thesol. As the coating dries, these low molecular weight species could riseto the coatings surface and modify the wettability of the coating andthereby alter its anti-soiling and/or self-cleaning properties.

Gel Permeation Chromatography (GPC) is a technique that is used tocharacterize the molecular weight of polymers. We have used Waters GPCsystems for molecular weight analysis. The method details are as followsHPLC system: a 1515 isocratic pump equipped with 2707 Autosampler and 50uL loop, 2414 RI detector with column heater. Column and detector ovenheated to 40° C. Flow used was 1.0 ml/min. Four 4.6×300 mm GPC Styrenedivinylbenzene copolymer packed columns in-line for an effective MWrange were used. The columns came pre-equilibrated in THF and THF wasused as the eluent. Polystyrene narrow standards were used and thestandard curve was fit to a 3rd-order polynomial. Nine polystyrenestandards from approx. 530 MW to 50,000 were used. The Poly Styrenestandards were prepared at 10 mg/ml each in THF and diluted theirsamples 1:10 in THF for injections. Results are shown in FIG. 7 a andFIG. 7 b for sol made from Example 2. It can be seen that some of thesols used for preparation of coatings in this disclosure can have aweight average Molecular Weight (Mw) of less than 1000 and numberaverage molecular weight of (Mn) of less than 1000 with polydispersity(PD) of less than 1.2.

Yet another way to modulate the abrasion resistance of the coatings ofthe present disclosure is by changing the temperature at which thecoatings are cured after drying. Similar films when cured at ambienttemperature typically will have a lower abrasion resistance compared tofilms cured at 120° C. which can be lower than films cured at 200° C. or300° C. in a conventional oven.

In general, the various coatings of the present disclosure provide ameans of making a transparent substrate or glass transmit more photonswithout altering its intrinsic structure and other properties, alongwith passivating the surface so that it becomes resistant to theadhesion of water, dirt, soil, and other exogenous matter. Accordingly,the coating mixtures and resulting gels and coatings as described hereinhave numerous commercial applications.

Regarding the coating mixtures themselves, these may be packaged forcommercial sale as a coating mixture or commercial coating formulationfor others to use. For example, the coating mixtures may be provided asa liquid composition, for example, for subsequent small scale treatmentof glass in a treatment separate from their usage as windows in solar orarchitectural systems. In this case the coating mixture may be packagedfor sale as siloxane polymer mixture after the silane precursors havebeen hydrolyzed and partially condensed.

In addition, the coating mixtures may be deposited and allowed to cureon a particular substrate that is subsequently packaged for sale as afinished assembly. In particular, the coating compositions of thepresent disclosure can be coated onto any transparent substrate that hashydrogen bond donor or hydrogen bond acceptor groups on the surface. Forexample, the coating can be applied as a treatment for a given glass orother transparent substrate before or after it has been integrated intoa device, such a solar cell, optical window or enclosure, for example,as part of a glass treatment process. In other embodiments, thedisclosure provides for the use of the coating compositions as anefficiency enhancement aid in architectural windows in building andhouses by the provision of anti-reflection benefits and/or by theprovision of anti-soiling benefits to augment the anti-reflectionbenefits. In other embodiments, the disclosure provides for the use ofthe coating compositions as an efficiency enhancement aid in treatmentof transparent surfaces that require regular cleaning to make themself-cleaning. For example, the coatings can be used in conjunction withglass used in windows, windshields, screens, architecture, goggles,eyeglasses, etc.

In other embodiments, the disclosure provides for the use of the coatingcompositions as an efficiency enhancement aid in photovoltaic solarmodule assemblies (e.g., the outer cover of solar modules) by theprovision of anti-reflection benefits and/or by the provision ofanti-soiling benefits to augment the anti-reflection benefits. Thesedevices convert solar energy into electrical energy and rely uponefficient absorption of photons, and effects such as reflection,scattering, and loss of absorption due to adsorbed soil or dirtparticles can lead to reduced power output. As noted, the coatings ofthis disclosure when coated onto a glass surface reduces reflection ofphotons (the so-called anti-reflective property) and also reducesadsorption and binding of dirt, soil, and other particulate matter fromthe environment to boost the transmission of photons through the glassas well as to prevent reduction in photons associated with deposition ofparticulate matter onto the surface.

The coatings for solar module applications provide unique challengesthat are not present with coatings typically utilized in other commonapplications. The use of anti-reflective coating in solar modulesnecessitates long term exposure of solar radiation that usually resultsin extensive degradation of polymeric materials under prolonged UVexposure due to photolytic breakdown of bonds in these materials. Thecoating compositions of the present disclosure utilize silane precursorsthat when hydrolyzed, condensed and cured give rise to a network that issimilar to glass with Si—O—Si bonds that are stable to radiativebreakdown. An additional advantage of using silica based materials insolar applications is the intrinsic hardness of the material that makesthe coating resistant to scratches, indentations, and abrasion. Further,the coatings of the present disclosure provide for enhanced lighttransmittance across the entire solar region from about 350 nm to about1150 nm, which is desirable for solar applications.

Further, the siloxane polymer mixture resulting from the coatingcompositions of this disclosure do not need to be applied to the solarmodules during manufacturing and may be applied after manufacturing toavoid any interference with the solar module manufacturing process. Itis expected that the solar module maker themselves may be able to usethe composition of this disclosure to coat the modules at appropriatepoints within their manufacturing process. In such instances, theprovision of a stable siloxane polymer mixture, that can be usedaccording to the methods described herein, provides a direct means forthe applying the coating mixture after manufacture of the modules oreven after final installation of the modules. This may streamline themanufacturing process and enhance the economic value of existingmodules, either existing inventory or modules already installed and inuse, to which the coatings can be applied.

In one embodiment, the process of coating the solar modules consists ofpreparing the module surface, coating the surface with the finalsiloxane polymer mixture made in accordance with the present disclosure,drying the coating under ambient conditions, and curing the driedmodules at elevated temperature. The module surface is prepared bypolishing the module with a cerium oxide slurry, followed by washing themodule with water, and drying it under ambient temperature-pressureconditions for a period ranging from about 10 hours to about 12 hours.

Once the module surface is prepared, in one embodiment, the finalsiloxane polymer mixture of the present disclosure is deposited ontosolar modules by means of a flow coater. The siloxane polymer mixture isdeposited onto the modules via gravitational free flow of the liquidsiloxane polymer mixture from top to bottom. The solar modules areplaced on the mobile platform that moves at a rate that is optimal forthe free flow of the siloxane polymer mixture without introducing breakpoints in the liquid stream or introducing turbulent flow. The rate ofliquid flow and the rate of movement of platform carrying the solarmodule are optimized for deposition of uniform, crack-free coatings thatare homogenous, free of deformities, and characterized by uniformthickness.

More specifically, in one embodiment, the module is placed on a mobilestage that is connected to a computer and programmed to move at a speedranging, in some embodiments, from about 0.05 cm/s to about 300 cm/s, inother embodiments from about 0.1 cm/s to about 10 cm/s, and in otherembodiments from about 0.25 cm/s to about 0.5 cm/s. The siloxane polymermixture is then deposited onto the module surface using a computercontrolled nozzle dispensing unit such that the rate of flow of siloxanepolymer mixture is, in some embodiments, from about 5 ml/min to about 50ml/min, in other embodiments from about 5 ml/min to about 25 ml/min, andin other embodiments from about 10 ml/min to about 15 ml/min. The rateat which the siloxane polymer mixture is deposited is important forproper deposition of the coatings. Notably, the nozzle diameter of thesol can be adjusted to ensure appropriate flow rate, with diameters ofthe nozzle ranging from about 0.3 mm to about 0.9 mm.

A particularly advantageous aspect of using a siloxane polymer mixtureis that it is in a liquid state but is also viscous enough to spreadwithout breakdown of the stream. The uniformity of the coatings isfurther ensured by adjusting the flow rate and the rate of the movementof the platform containing the solar modules. For a given flow rate ofthe siloxane polymer mixture, if the rate of the movement of theplatform is too fast then it leads to rupture of the siloxane polymermixture stream causing uneven coatings. For a given flow rate of thesiloxane polymer mixture, if the rate of the movement of the platform istoo slow it results in excessive flow and material build up thatdeteriorates the uniformity of the films. Therefore, a specific optimumof siloxane polymer mixture flow rate and the platform movement areimportant to provide even, uniform, and homogenous coatings. The use ofspecific pH, solvent, and silane concentrations as outlined aboveprovide the ideal viscosities.

The coating process is also facilitated by the evaporation of thesolvent during the flow of the siloxane polymer mixture onto the panel,which also affects the development of uniform films or coatings on themodule surface. The coatings are formed when the free flowing siloxanepolymer mixture dries on the surface and forms a solid on the glasssurface. More specifically, the bottom edge of the sol represents theleading wet line while drying occurs at the top edge. As the solventevaporates, the siloxane polymer mixture becomes more viscous andfinally sets at the top edge while the bottom edge is characterized byliquid edge spreading. The spreading liquid at the bottom edge enablesthe free flow of the siloxane polymer mixture while the setting siloxanepolymer mixture at the top edge fixes the materials and preventsformation of lamellar structures. A balance of these factors isimportant for formation of uniform films.

The flow coating method does not allow seepage of the siloxane polymermixture into the internal parts of the solar module assembly as theexcess siloxane polymer mixture can be collected into a container at thebottom of the assembly and recycled. Similarly, it does not facilitatecorrosion and/or leaching of the chemicals from the interior of thesolar module assembly. The flow coater method exposes only the glassside to the siloxane polymer mixture while the other side of the moduleassembly, which may contain with electrical contacts and leads does notcome into any contact with the liquid siloxane polymer mixture. As such,the flow coating process is particular beneficial to coating solarmodules during either the assembly or the post-assembly stages.

The methods described here can be used to coat solar modules of variablesizes and in variable configurations. For example, typical modules havethe dimensions of about 1 m×1.6 m, which can be coated either inportrait configuration or landscape configurations mode via appropriateplacement in the mobile platform.

The flow coater can be used to coat the modules at the rate of about15-60 modules per hour. The rate of coating of individual modules woulddepend upon the size of the modules and whether they are coated in theportrait mode or landscape orientation. Additionally, multiple coatersoperating in parallel, or a single coater that runs along the entirelength can be used in conjunction with the module assembly line toincrease the production rate.

After depositing the coating, the module is dried for a period rangingfrom about 1 minute to about 20 minutes or longer under ambientconditions. The coated module is then cured using any of the techniquesfor curing described above, after which the coated module is ready foruse.

The anti-reflecting coatings described herein increase the peak power ofthe solar cells by approximately 3% due to the anti-reflective property.In addition, it is estimated that the anti-soiling property wouldcontribute to minimize transmissive losses associated with accumulationof dirt on the modules. Typical soiling losses are estimated at about 5%and use of these coatings is expected to reduce the losses in half.

Examples

The following describes various aspects of the coatings made accordingto certain embodiments of the disclosure in connection with the Figures.These examples should not be viewed as limiting. The general procedureused for the preparation of sol from a two-part process of acidcatalyzed hydrolysis of organosilane, alkoxysilane and/ororganofluorosilane is described as follows:

In Method I, in the first part of a two-part process, a first sol calledSol I is prepared by charging a 500 ml flask with deionized water (DIW),hydrochloric acid (HCl), optional additive(s) and IPA, then stirring at100 rpm at room temperature for one minute followed by addition ofmethyltrialkoxysilane, then stirring at about 100 rpm at roomtemperature for 30 minutes. A second sol called Sol II is prepared bycharging a 500 ml flask with DIW, HCl and IPA, then stirring at 100 rpmfor one minute followed by addition of (3,3,3trifluoropropyl)-trimethoxysilane, then stirring at about 100 rpm atroom temperature for 30 minutes. In the second part of the two-partprocess, Sol I and Sol II are combined and tetraalkoxysilane is added tothis mixture and stirred for 30 minutes at about 100 rpm at roomtemperature. The final sol mixture is aged for 48 hours at roomtemperature and then characterized by GPC and NMR.

In Method II, in the first part of a two-part process, a 500 ml flask ischarged with DIW, HCl, optional additive(s), and IPA, then stirred at100 rpm at room temperature for one minute followed by addition ofmethyltrialkoxysilane, then stirred at about 100 rpm at room temperaturefor 30 minutes. In the second part of the two-part process,tetraalkoxysilane is added to this mixture and stirred for 30 minutes atabout 100 rpm at room temperature. The final sol mixture is aged for 48hours at room temperature and then characterized by GPC and NMR.

In Method III, in the first part of a two-part process, a 500 ml flaskis charged with DIW, HCl, optional additive(s), and IPA, then stirred at100 rpm at room temperature for one minute followed by addition oftetraalkoxysilane, then stirred at about 100 rpm at room temperature for30 minutes. In the second part of the two-part process,methyltrialkoxysilane is added to this mixture and stirred for 30minutes at about 100 rpm at room temperature. The final sol mixture isaged for 48 hours at room temperature and then characterized by GPC andNMR.

In Method IV, in the first part of a two-part process, a 500 ml flask ischarged with DIW, HCl, optional additive(s), and IPA, then stirred at100 rpm at room temperature for one minute followed by addition oftetraalkoxysilane then stirred at about 100 rpm at room temperature for30 minutes. In the second part of the two-part process, a mixture of(3,3,3 trifluoropropyl)-trimethoxysilane and methyltrialkoxysilane isadded and stirred for 30 minutes at about 100 rpm at room temperature.The final sol mixture is aged for 48 hours at room temperature and thencharacterized by GPC and NMR.

In an embodiment referred to as Example 1, following Method I, Sol I isprepared by charging a 500 mL flask with 177 g of IPA and 25 g of 0.04 MHCl. After stirring at 100 rpm at room temperature for one minute, 2.87g (0.021 moles) of methyltrimethoxysilane is added to the mixture. Themixture is stirred at room temperature for 30 minutes. Sol II isprepared by charging a 500 mL flask with 177 g of IPA and 25 g of 0.04 MHCl. After stirring at 100 rpm at room temperature for one minute, 3.71g (0.021 moles) of (3,3,3-trifluoropropyl)-trimethoxysilane is added tothe mixture. The mixture is stirred at room temperature for 30 minutes.Sol I and II are mixed together followed by addition of 6.39 g (0.042moles) of tetramethoxysilane. The final mixture is stirred at roomtemperature for 30 minutes. This mixture is allowed to age under ambientconditions for 24 hours up to 120 hours. After aging the solformulation, 30×30 cm glass sheets (polished with cerium oxide polish,washed, and allowed to dry) are flow coated with the final sol mixtureand allowed to dry for approximately 1-10 minutes followed by curing attemperature of 120° C. for 60 minutes.

In an embodiment referred to as Example 2, following Method I, Sol I isprepared by charging a 500 mL flask with 177 g of IPA and 25 g of 0.04 MHCl. After stirring at 100 rpm at room temperature for one minute, 2.87g (0.021 moles) of methyltrimethoxysilane is added to the mixture. Themixture is stirred at room temperature for 30 minutes. Sol II isprepared by charging a 500 mL flask with 177 g of IPA and 25 g of 0.04 MHCl. After stirring at 100 rpm at room temperature for one minute, 3.71g (0.021 moles) of (3,3,3-trifluoropropyl)-trimethoxysilane is added tothe mixture. The mixture is stirred at room temperature for 30 minutes.Sol I and II are mixed together followed by addition of 8.8 g (0.042moles) of tetraethoxysilane. The final mixture is stirred at roomtemperature for 30 minutes. This mixture is allowed to age under ambientconditions for 48 hours. The GPC test of the final sol producedmolecular weight of Mw=1,174 g/mol with polydispersity PD=1.13. Afteraging the sol formulation, 30×30 cm glass sheets (polished with ceriumoxide polish, washed, and allowed to dry) are flow coated with the finalsol mixture and allowed to dry for approximately 1-10 minutes followedby curing at temperature of 120° C. for 60 minutes. Typical GPC resultsare shown in FIGS. 7 a-1 and 7 a-2 and the Si-NMR results are shown inFIG. 21. An SEM cross-section of a representative sample of cured filmfrom example 2 is shown in FIG. 4.

A TEM cross-section of a representative sample of the dried and curedfilm from Example 2 is shown in FIG. 3 a. TEM cross-section and the HighResolution TEM of the film from Example 2 show no evidence of long rangeorder within the film. The film morphology at a scale 5 nm shows littleevidence of porosity.

In an embodiment referred to as Example 3, following Method II the solis prepared by charging a 500 mL flask with 354 g of IPA and 50 g of0.04 M HCl. After stirring at 100 rpm at room temperature for oneminute, 4.37 g (0.0321 moles) of methyltrimethoxysilane is added to themixture. The mixture is stirred at room temperature for 30 minutesfollowed by addition of 7.08 g (0.034 moles) of tetraethoxysilane. Thefinal mixture is stirred at room temperature for 30 minutes. Thismixture is allowed to age under ambient conditions for 48 hours. The GPCtest of the final sol produced molecular weight of Mw=902 g/mol withpolydispersity PD=1.14. 30×30 cm glass sheets (polished with ceriumoxide polish, washed, and allowed to dry) are flow coated with the finalsol mixture and allowed to dry for approximately 1-10 minutes followedby curing at temperature of 120° C. for 60 minutes. GPC results areshown in FIGS. 7 b-1 and 7 b-2, and NMR results are shown in FIG. 22.SEM cross-section of a representative sample of cured film from Example3 is shown in FIG. 5.

In an embodiment referred to as Example 4, following Method I, Sol I isprepared by charging a 500 mL flask with 177 g of IPA and 25 g of 0.04 MHCl. After stirring at 100 rpm at room temperature for one minute, 2.63g (0.0193 moles) of methyltrimethoxysilane is added to the mixture. Themixture is stirred at room temperature for 30 minutes. Sol II isprepared by charging a 500 mL flask with 177 g of IPA and 25 g of 0.04 MHCl. After stirring at 100 rpm at room temperature for one minute, 0.284g (0.0013 moles) of (3,3,3-trifluoropropyl)-trimethoxysilane is added tothe mixture. The mixture is stirred at room temperature for 30 minutes.Sol I and II are mixed together followed by addition of 6.24 g (0.03moles) of tetraethoxysilane. The final mixture is stirred at roomtemperature for 30 minutes. This mixture is allowed to age under ambientconditions for 48 hours. The GPC test of the final sol producedmolecular weight of Mw=690 g/mol with polydispersity PD=1.10. 30×30 cmglass sheets (polished with cerium oxide polish, washed, and allowed todry) are flow coated with the final sol mixture and allowed to dry forapproximately 1-10 minutes followed by curing at temperature of 120° C.for 60 minutes. GPC results are shown in FIGS. 7 c-1 and 7 c-2. SEMcross-section of a representative sample of cured film from Example 4 isshown in FIG. 6.

In an embodiment referred to as Example 5, following Method I, Sol I isprepared by charging a 500 mL flask with 177 g of IPA and 25 g of 0.04 MHCl. After stirring at 100 rpm at room temperature for one minute, 2.39g (0.01753 moles) of methyltrimethoxysilane is added to the mixture. Themixture is stirred at room temperature for 30 minutes. Sol II isprepared by charging a 500 mL flask with 177 g of IPA and 25 g of 0.04 MHCl. After stirring at 100 rpm at room temperature for one minute, 0.399g (0.00262 moles) of (3,3,3-trifluoropropyl)-trimethoxysilane is addedto the mixture. The mixture is stirred at room temperature for 30minutes. Sol I and II are mixed together followed by addition of 6.24 g(0.03 moles) of tetraethoxysilane. The final mixture is stirred at roomtemperature for 30 minutes. This mixture is allowed to age under ambientconditions for 48 hours. The GPC test of the final sol producedmolecular weight of Mw=1,190 g/mol with polydispersity PD=1.21. 30×30 cmglass sheets (polished with cerium oxide polish, washed, and allowed todry) are flow coated with the final sol mixture and allowed to dry forapproximately 1-10 minutes followed by curing at temperature of 120° C.for 60 minutes. GPC results are shown in FIGS. 7 d-1 and 7 d-2.

In an embodiment referred to as Example 6, following Method I, sol I isprepared by charging a 500 mL flask with 177 g of IPA and 25 g of 0.04 MAcOH (acetic acid). After stirring at 100 rpm at room temperature forone minute, 2.32 g (0.017 moles) of methyltrimethoxysilane is added tothe mixture. The mixture is stirred at room temperature for 30 minutes.Sol II is prepared by charging a 500 mL flask with 177 g of IPA and 25 gof 0.08 M AcOH. After stirring at 100 rpm at room temperature for oneminute, 3.71 g (0.017 moles) of (3,3,3-trifluoropropyl)-trimethoxysilaneis added to the mixture. The mixture is stirred at room temperature for30 minutes. Sol I and II are mixed together followed by addition of 7.08g (0.034 moles) of tetraethoxysilane. The final mixture is stirred atroom temperature for 30 minutes. This mixture is allowed to age underambient conditions for 48 hours. The GPC test of the final sol producedmolecular weight of Mw=2,374 g/mol with polydispersity PD=2.35. 30×30 cmglass sheets (polished with cerium oxide polish, washed, and allowed todry) are flow coated with the final sol mixture and allowed to dry forapproximately 1-10 minutes followed by curing at temperature of 120° C.for 60 minutes. GPC results are shown in FIGS. 7 e-1 and 7 e-2.

In an embodiment referred to as Example 7, following method II the solis prepared by charging a 500 mL flask with 354 g of IPA and 50 g of0.08 M AcOH. After stirring at 100 rpm at room temperature for oneminute, 9.13 g (0.067 moles) of methyltrimethoxysilane is added to themixture. The mixture is stirred at room temperature for 30 minutesfollowed by addition of 13.96 g (0.067 moles) of tetraethoxysilane. Thefinal mixture is stirred at room temperature for 30 minutes. Thismixture is allowed to age under ambient conditions for 48 hours. The GPCtest of the final sol produced molecular weight of Mw=926 g/mol withpolydispersity PD=1.32. 30×30 cm glass sheets (polished with ceriumoxide polish, washed, and allowed to dry) are flow coated with the finalsol mixture and allowed to dry for approximately 1-10 minutes followedby curing at temperature of 120° C. for 60 minutes. GPC results areshown in FIGS. 7 f-1 and 7 f-2.

In an embodiment referred to as Example 8, following Method II the solis prepared by charging a 500 mL flask with 354 g of IPA and 50 g of0.08 M HCl. After stirring at 100 rpm at room temperature for oneminute, 9.13 g (0.067 moles) of methyltrimethoxysilane is added to themixture. The mixture is stirred at room temperature for 30 minutesfollowed by addition of 13.96 g (0.067 moles) of tetraethoxysilane. Thefinal mixture is stirred at room temperature for 30 minutes. Thismixture is allowed to age under ambient conditions for 48 hours. The GPCtest of the final sol produced molecular weight of Mw=806 g/mol withpolydispersity PD=1.09. 30×30 cm glass sheets (polished with ceriumoxide polish, washed, and allowed to dry) are flow coated with the finalsol mixture and allowed to dry for approximately 1-10 minutes followedby curing at temperature of 120° C. for 60 minutes. GPC results areshown in FIGS. 7 g-1 and 7 g-2. FIG. 26 and FIG. 27 show the results ofextended shelf life testing of 6 months aging at 20° C. and of 7 daysaging at 40° C. respectively. The data shows this formulation hasexcellent shelf life stability.

In an embodiment referred to as Example 9, following Method II the solis prepared by charging a 500 mL flask with 354 g of IPA and 50 g of0.08 M HCl. After stirring at 100 rpm at room temperature for oneminute, 9.13 g (0.067 moles) of methyltrimethoxysilane is added to themixture. The mixture is stirred at room temperature for 30 minutesfollowed by addition of 13.96 g (0.067 moles) of tetraethoxysilane. Thefinal mixture is stirred at room temperature for 30 minutes. Thismixture is allowed to age under ambient conditions for 48 hours. The GPCtest of the final sol produced molecular weight of Mw=857 g/mol withpolydispersity PD=1.15. 30×30 cm glass sheets (polished with ceriumoxide polish, washed, and allowed to dry) are flow coated with the finalsol mixture and allowed to dry for approximately 1-10 minutes followedby curing at temperature of 120° C. for 60 minutes. GPC results areshown in FIGS. 7 h-1 and 7 h-2.

In an embodiment referred to as Example 10, following Method II the solis prepared by charging a 500 mL flask with 197 g of IPA and 140 g of0.08 M HCl. After stirring at 100 rpm at room temperature for oneminute, 30.2 g (0.288) of methyltrimethoxysilane is added to themixture. The mixture is stirred at room temperature for 30 minutesfollowed by addition of 60 g (0.288 moles) of tetraethoxysilane. Thefinal mixture is stirred at room temperature for 30 minutes. Thismixture is allowed to age under ambient conditions for 48 hours. The GPCtest of the final sol produced molecular weight of Mw=1,635 g/mol withpolydispersity PD=1.36. 30×30 cm glass sheets (polished with ceriumoxide polish, washed, and allowed to dry) are flow coated with the finalsol mixture and allowed to dry for approximately 1-10 minutes followedby curing at temperature of 120° C. for 60 minutes. GPC results areshown in FIGS. 7 k-1 and 7 k-2.

In an embodiment referred to as Example 11, sol from Example 8 isformulated with 6.4 g of TWEEN 80. 30×30 cm glass sheets (polished withcerium oxide polish, washed, and allowed to dry) are flow coated withthe final sol mixture and allowed to dry for approximately 1-10 minutesfollowed by thermal curing. An SEM cross-section of a representativesample of cured film on float glass from Example 11 is shown in FIG. 24and a representative sample of cured film on float glass from Example 11is shown in FIG. 25.

In an embodiment referred to as Example 12, sol from Example 8 isformulated with 4.27 g of TWEEN 80. 30×30 cm glass sheets (polished withcerium oxide polish, washed, and allowed to dry) are flow coated withthe final sol mixture and allowed to dry for approximately 1-10 minutesfollowed by thermal curing.

In an embodiment referred to as Example 13, sol from Example 8 isformulated with 2.14 g of TWEEN 80. 30×30 cm glass sheets (polished withcerium oxide polish, washed, and allowed to dry) are flow coated withthe final sol mixture and allowed to dry for approximately 1-10 minutesfollowed by thermal curing.

In an embodiment referred to as Example 14, following Method II the solis prepared by charging a 500 mL flask with 354 g of IPA, 0.66 g (0.011moles) of B(OH)₃ and 50 g of 0.08 M HCl. After stirring at 100 rpm atroom temperature for one minute, 9.13 g (0.067 moles) ofmethyltrimethoxysilane is added to the mixture. The mixture is stirredat room temperature for 30 minutes followed by addition of 13.96 g(0.067 moles) of tetraethoxysilane. The final mixture is stirred at roomtemperature for 30 minutes. This mixture is allowed to age under ambientconditions for 48 hours. The GPC test of the final sol producedmolecular weight of Mw=826/mol with polydispersity PD=1.07. 30×30 cmglass sheets (polished with cerium oxide polish, washed, and allowed todry) are flow coated with the final sol mixture and allowed to dry forapproximately 1-10 minutes followed by thermal curing.

In an embodiment referred to as Example 15, sol from Example 8 isformulated with 6.4 g of TWEEN 80 and 6.4 g of AlCl₃. 30×30 cm glasssheets (polished with cerium oxide polish, washed, and allowed to dry)are flow coated with the final sol mixture and allowed to dry forapproximately 1-10 minutes followed by thermal curing.

In an embodiment referred to as Example 16, sol from Example 8 isformulated with 6.4 g of TWEEN 20. 30×30 cm glass sheets (polished withcerium oxide polish, washed, and allowed to dry) are flow coated withthe final sol mixture and allowed to dry for approximately 1-10 minutesfollowed by thermal curing.

In an embodiment referred to as Example 17, sol from Example 8 isformulated with 4.27 g of TWEEN 20. 30×30 cm glass sheets (polished withcerium oxide polish, washed, and allowed to dry) are flow coated withthe final sol mixture and allowed to dry for approximately 1-10 minutesfollowed by thermal curing.

In an embodiment referred to as Example 18, sol from Example 8 isformulated with 2.14 g of TWEEN 20. 30×30 cm glass sheets (polished withcerium oxide polish, washed, and allowed to dry) are flow coated withthe final sol mixture and allowed to dry for approximately 1-10 minutesfollowed by thermal curing.

In an embodiment referred to as Example 19, sol from Example 8 isformulated with 6.4 g of PEG 600. 30×30 cm glass sheets (polished withcerium oxide polish, washed, and allowed to dry) are flow coated withthe final sol mixture and allowed to dry for approximately 1-10 minutesfollowed by thermal curing. An SEM cross-section of a representativesample of cured film on float glass from Example 19 is shown in FIG. 23.

In an embodiment referred to as Example 20, sol from Example 8 isformulated with 6.4 g of PEG 400. 30×30 cm glass sheets (polished withcerium oxide polish, washed, and allowed to dry) are flow coated withthe final sol mixture and allowed to dry for approximately 1-10 minutesfollowed by thermal curing.

In an embodiment referred to as Example 21, sol from Example 8 isformulated with 6.4 g of PEG 300. 30×30 cm glass sheets (polished withcerium oxide polish, washed, and allowed to dry) are flow coated withthe final sol mixture and allowed to dry for approximately 1-10 minutesfollowed by thermal curing.

In an embodiment referred to as Example 22, following Method II the solis prepared by charging a 500 mL flask with 354 g of IPA, 6.4 g of TWEEN80 and 50 g of 0.08 M HCl. After stirring at 100 rpm at room temperaturefor one minute, 9.13 g (0.067 moles) of methyltrimethoxysilane is addedto the mixture. The mixture is stirred at room temperature for 30minutes followed by addition of 13.96 g (0.067 moles) oftetraethoxysilane. The final mixture is stirred at room temperature for30 minutes. This mixture is allowed to age under ambient conditions for48 hours. The GPC test of the final sol produced molecular weight ofMw=1558 g/mol with polydispersity PD=1.34. 30×30 cm glass sheets(polished with cerium oxide polish, washed, and allowed to dry) are flowcoated with the final sol mixture and allowed to dry for approximately1-10 minutes followed by thermal curing.

In an embodiment referred to as Example 23, following Method II the solis prepared by charging a 500 mL flask with 354 g of IPA, 6.4 g of PEG600 and 50 g of 0.08 M HCl. After stirring at 100 rpm at roomtemperature for one minute, 9.13 g (0.067 moles) ofmethyltrimethoxysilane is added to the mixture. The mixture is stirredat room temperature for 30 minutes followed by addition of 13.96 g(0.067 moles) of tetraethoxysilane. The final mixture is stirred at roomtemperature for 30 minutes. This mixture is allowed to age under ambientconditions for 48 hours. The GPC test of the final sol producedmolecular weight of Mw=988 g/mol with polydispersity PD=1.1. 30×30 cmglass sheets (polished with cerium oxide polish, washed, and allowed todry) are flow coated with the final sol mixture and allowed to dry forapproximately 1-10 minutes followed by thermal curing.

In an embodiment referred to as Example 24, following Method II the solis prepared by charging a 500 mL flask with 354 g of IPA, 6.4 g ofPEG-b-PPG-b-PEG and 50 g of 0.08 M HCl. After stirring at 100 rpm atroom temperature for one minute, 9.13 g (0.067 moles) ofmethyltrimethoxysilane is added to the mixture. The mixture is stirredat room temperature for 30 minutes followed by addition of 13.96 g(0.067 moles) of tetraethoxysilane. The final mixture is stirred at roomtemperature for 30 minutes. This mixture is allowed to age under ambientconditions for 48 hours. The GPC test of the final sol producedmolecular weight of Mw=1333 g/mol with polydispersity PD=1.17. 30×30 cmglass sheets (polished with cerium oxide polish, washed, and allowed todry) are flow coated with the final sol mixture and allowed to dry forapproximately 1-10 minutes followed by thermal curing.

In an embodiment referred to as Example 25, a 500 mL three-necked flaskfitted with two addition funnels and a thermocouple temperature sensoris cooled in an ice bath. One of the addition funnels is charged with amixture 32 g (0.235 moles) of methyltrimethoxysilane, 29 g of IPA, and1.6 g of glacial AcOH. The other funnel is charged with 100 g of a 34%by weight colloidal silica (Nalco 1034A). The colloidal silica andmethyltrimethoxysilane solutions are added drop wise at such a rate thatthe temperature of the reaction mixture does not exceed 5° C. After theaddition is complete, the mixture is allowed to warm to ambienttemperature with continued stirring and allowed to stand overnight. Themixture (151 g) is diluted with IPA (757 g). This mixture is allowed toage under ambient conditions for 48 hours. The GPC test of the final solproduced molecular weight of Mw=685 g/mol with polydispersity PD=1.1.30×30 cm glass sheets (polished with cerium oxide polish, washed, andallowed to dry) are flow coated with the final sol mixture and allowedto dry for approximately 1-10 minutes followed by thermal curing.

In an embodiment referred to as Example 26, a 500 mL three-necked flaskfitted with two addition funnels and a thermocouple temperature sensoris cooled in an ice bath. One of the addition funnels is charged with amixture of 17 g (0.125 moles) of methyltrimethoxysilane, 29 g of IPA,and 1.68 g of glacial AcOH. The other funnel is charged with 100 g of a34% by weight colloidal silica (Nalco 1034A). The colloidal silica andmethyltrimethoxysilane solutions are added drop wise at such a rate thatthe temperature of the reaction mixture does not exceed 5° C. After theaddition is complete, the mixture is allowed to warm to ambienttemperature with continued stirring and allowed to stand overnight. Themixture (140 g) is diluted with IPA (853.5 g). This mixture is allowedto age under ambient conditions for 48 hours. The GPC test of the finalsol produced molecular weight of Mw=637 g/mol with polydispersityPD=1.07. 30×30 cm glass sheets (polished with cerium oxide polish,washed, and allowed to dry) are flow coated with the final sol mixtureand allowed to dry for approximately 1-10 minutes followed by thermalcuring.

In an embodiment referred to as Example 27, a 500 mL three-necked flaskfitted with two addition funnels and a thermocouple temperature sensoris cooled in an ice bath. One of the addition funnels is charged with amixture 8 g (0.059 moles) of methyltrimethoxysilane, 28 g of IPA, and1.68 g of glacial AcOH. The other funnel is charged with 100 g of 34% byweight colloidal silica (Nalco 1034A). The colloidal silica andmethyltrimethoxysilane solutions are added drop wise at such a rate thatthe temperature of the reaction mixture does not exceed 5° C. After theaddition is complete, the mixture is allowed to warm to ambienttemperature with continued stirring and allowed to stand overnight. Themixture (151 g) is diluted with IPA (757 g). This mixture is allowed toage under ambient conditions for 48 hours. The GPC test of the final solproduced molecular weight of Mw=567 g/mol with polydispersity PD=1.03.30×30 cm glass sheets (polished with cerium oxide polish, washed, andallowed to dry) are flow coated with the final sol mixture and allowedto dry for approximately 1-10 minutes followed by thermal curing.

In an embodiment referred to as Example 28. The final sol from Example27 is formulated with 1.79 g of 10 weight % solution of PowderLink inNMP. 30×30 cm glass sheets (polished with cerium oxide polish, washed,and allowed to dry) are flow coated with the final sol mixture andallowed to dry for approximately 1-10 minutes followed by thermalcuring.

In an embodiment referred to as Example 29. The final sol from Example23 is formulated with 1.79 g of 10 weight % solution of PowderLink inNMP. 30×30 cm glass sheets (polished with cerium oxide polish, washed,and allowed to dry) are flow coated with the final sol mixture andallowed to dry for approximately 1-10 minutes followed by thermalcuring.

In an embodiment referred to as Example 30. The final sol from Example23 is formulated with 3.58 g of 10 weight % solution of PowderLink inNMP. 30×30 cm glass sheets (polished with cerium oxide polish, washed,and allowed to dry) are flow coated with the final sol mixture andallowed to dry for approximately 1-10 minutes followed by thermalcuring.

In an embodiment referred to as Example 31. The final sol from Example11 is formulated with 2.17 g (0.0067 moles) of Al(acac)₃. 30×30 cm glasssheets (polished with cerium oxide polish, washed, and allowed to dry)are flow coated with the final sol mixture and allowed to dry forapproximately 1-10 minutes followed by thermal curing.

In an embodiment referred to as Example 32, following Method II the solis prepared by charging a 500 mL flask with 354 g of IPA, 8.09 g ofAlCl₃.6H₂O and 6.4 g of TWEEN 80 and 50 g of 0.08 M HCl. After stirringat 100 rpm at room temperature for one minute, 9.13 g (0.067 moles) ofmethyltrimethoxysilane is added to the mixture. The mixture is stirredat room temperature for 30 minutes followed by addition of 13.96 g(0.067 moles) of tetraethoxysilane. The final mixture is stirred at roomtemperature for 30 minutes. This mixture is allowed to age under ambientconditions for 48 hours. The GPC test of the final sol producedmolecular weight of Mw=1732 g/mol with polydispersity PD=1.41. 30×30 cmglass sheets (polished with cerium oxide polish, washed, and allowed todry) are flow coated with the final sol mixture and allowed to dry forapproximately 1-10 minutes followed by thermal curing.

In an embodiment referred to as Example 33, following Method III the solis prepared by charging a 500 ml flask with 345 g of IPA, and 50 g of0.08 M HCl. After stirring at 100 rpm at room temperature for oneminute, 13.96 g (0.067 moles) of tetraethoxysilane is added to themixture. The mixture is stirred at room temperature for 30 minutesfollowed by addition of 9.13 g (0.067 moles) of methyltrimethoxysilane.The final mixture is stirred at room temperature for 30 minutes. Thismixture is allowed to age under ambient conditions for 48 hours. The GPCtest of the final sol produced molecular weight of Mw=886 g/mol withpolydispersity PD=1.07. 30×30 cm glass sheets (polished with ceriumoxide polish, washed, and allowed to dry) are flow coated with the finalsol mixture and allowed to dry for approximately 1-10 minutes followedby thermal curing. NMR results are shown in FIG. 28.

In an embodiment referred to as Example 34, sol from Example 33 isformulated with 6.4 g of PEG 600. 30×30 cm glass sheets (polished withcerium oxide polish, washed, and allowed to dry) are flow coated withthe final sol mixture and allowed to dry for approximately 1-10 minutesfollowed by thermal curing.

In an embodiment referred to as Example 35, following Method III the solis prepared by charging a 500 ml flask with 345 g of IPA, and 50 g of0.08 M HCl. After stirring at 100 rpm at room temperature for oneminute, 12.6 g (0.061 moles) of tetraethoxysilane is added to themixture. The mixture is stirred at room temperature for 30 minutesfollowed by addition of 5.73 g (0.042 moles) of methyltrimethoxysilaneand 6.85 g (0.033 moles) of (3,3,3-trifluoropropyl)-trimethoxysilane.The final mixture is stirred at room temperature for 30 minutes. Thismixture is allowed to age under ambient conditions for 48 hours. The GPCtest of the final sol produced molecular weight of Mw=717 g/mol withpolydispersity PD=1.01. 30×30 cm glass sheets (polished with ceriumoxide polish, washed, and allowed to dry) are flow coated with the finalsol mixture and allowed to dry for approximately 1-10 minutes followedby thermal curing. NMR results are shown in FIG. 29.

In an embodiment referred to as Example 36, 100 g of sol from Example 8is formulated with 0.2 g of hydrogen peroxide and spin coated at 700(rotations per minutes) rpm for 40 seconds on a 10×10 cm glass sheetfollowed by thermal curing.

In an embodiment referred to as Example 37, 100 g of sol from Example 8is formulated with 0.3 g of hydrogen peroxide and spin coated at 700 rpmfor 40 seconds on a 10×10 cm glass sheet followed by thermal curing.

In an embodiment referred to as Example 38, 100 g of sol from Example 8is formulated with 0.4 g of hydrogen peroxide and spin coated at 700 rpmfor 40 seconds on a 10×10 cm glass sheet followed by thermal curing.

In an embodiment referred to as Example 39, 100 g of sol from Example 8is formulated with 0.2 g of benzoyl peroxide and spin coated at 700 rpmfor 40 seconds on a 10×10 cm glass sheet followed by thermal curing.

In an embodiment referred to as Example 40, 100 g of sol from Example 8is formulated with 0.3 g of benzoyl peroxide and spin coated at 700 rpmfor 40 seconds on a 10×10 cm glass sheet followed by thermal curing.

In an embodiment referred to as Example 41, 100 g of sol from Example 8is formulated with 0.4 g of benzoyl peroxide and spin coated at 700 rpmfor 40 seconds on a 10×10 cm glass sheet followed by thermal curing.

In an embodiment referred to as Example 42, 100 g of sol from Example 8is formulated with 0.2 g of AIBN (Azobisisobutyronitrile) and spincoated at 700 rpm for 40 seconds on a 10×10 cm glass sheet followed bythermal curing.

In an embodiment referred to as Example 43, 100 g of sol from Example 8is formulated with 0.3 g of AIBN (Azobisisobutyronitrile) and spincoated at 700 rpm for 40 seconds on a 10×10 cm glass sheets followed bythermal curing.

In an embodiment referred to as Example 44, 100 g of sol from Example 8is formulated with 0.4 g of AIBN (Azobisisobutyronitrile) and spincoated at 700 rpm for 40 seconds on a 10×10 cm glass sheet followed bythermal curing.

In an embodiment referred to as Example 45, 100 g of sol from Example 8is formulated with 0.2 g of dicumyl peroxide (DCP) and spin coated at700 rpm for 40 seconds on a 10×10 cm glass sheet followed by thermalcuring.

In an embodiment referred to as Example 46, 100 g of sol from Example 8is formulated with 0.3 g of dicumyl peroxide (DCP) and spin coated at700 rpm for 40 seconds on a 10×10 cm glass sheet followed by thermalcuring.

In an embodiment referred to as Example 47, 100 g of sol from Example 8is formulated with 0.4 g of dicumyl peroxide (DCP) and spin coated at700 rpm for 40 seconds on a 10×10 cm glass sheet followed by thermalcuring.

In an embodiment referred to as Example 48, 100 g of sol from Example 8is formulated with 0.2 g of dicumyl peroxide (DCP) and 0.6 g of NMP. Theresulting mixture is spin coated at 700 rpm for 40 seconds on a 10×10 cmglass sheet followed by thermal curing.

In an embodiment referred to as Example 49, 100 g of sol from Example 8is formulated with 0.2 g of dicumyl peroxide (DCP) and 0.6 g of THF. Theresulting mixture is spin coated at 700 rpm for 40 seconds on a 10×10 cmglass sheet followed by thermal curing.

In an embodiment referred to as Example 50, 100 g of sol from Example 8is formulated with 0.2 g of dicumyl peroxide (DCP) and 0.6 g of PGME.The resulting mixture is spin coated at 700 rpm for 40 seconds on a10×10 cm glass sheet followed by thermal curing.

In an embodiment referred to as Example 51, 100 g of sol from Example 8is formulated with 0.2 g of dicumyl peroxide (DCP) and 2 g of PGME. Theresulting mixture is spin coated at 700 rpm for 40 seconds on a 10×10 cmglass sheet followed by thermal curing.

In an embodiment referred to as Example 52, 100 g of sol from Example 8is formulated with 0.8 g of glyoxal. The resulting mixture is spincoated at 700 rpm for 40 seconds on a 10×10 cm glass sheet followed bythermal curing.

In an embodiment referred to as Example 53, 100 g of sol from Example 8is formulated with 0.2 g of dicumyl peroxide (DCP) and 2 g of PGME and0.8 g of glyoxal. The resulting mixture is spin coated at 700 rpm for 40seconds on a 10×10 cm glass sheet followed by thermal curing. It wasalso roll-coated onto a substrate heated to 40° C. then cured at 275° C.for 30 minutes. The roll-coated sample was examined by SEM and isdepicted in FIG. 32.

In an embodiment referred to as Example 54, following Method II the solis prepared by charging a 500 mL flask with 354 g of IPA and 50 g of0.08 M HCl. After stirring at 100 rpm at room temperature for oneminute, 9.13 g (0.067 moles) of methyltrimethoxysilane is added to themixture. The mixture is stirred at room temperature for 30 minutesfollowed by addition of 13.96 g (0.067 moles) of tetraethoxysilane and7.64 g of PGME. The final mixture is stirred at room temperature for 30minutes. This mixture is allowed to age under ambient conditions for 48hours. The final sol is spin coated at 700 rpm for 40 seconds on a 10×10cm glass sheet followed by thermal curing.

In an embodiment referred to as Example 55, 100 g of sol from Example 54is formulated with 0.2 g of dicumyl peroxide (DCP) and 0.8 g of glyoxal.The resulting mixture is spin coated at 700 rpm for 40 seconds on a10×10 cm glass sheet followed by thermal curing. It was also roll-coatedonto a substrate at room temperature, then cured at 275° C. for 30minutes. The roll-coated sample was examined by SEM and is depicted inFIG. 30.

In an embodiment referred to as Example 56, following Method II the solis prepared by charging a 500 mL flask with 354 g of IPA and 50 g of0.08 M HCl. After stirring at 100 rpm at room temperature for oneminute, 9.13 g (0.067 moles) of methyltrimethoxysilane is added to themixture. The mixture is stirred at room temperature for 30 minutesfollowed by addition of 13.96 g (0.067 moles) of tetraethoxysilane and7.64 g of PGME and 3.06 g of glyoxal. The final mixture is stirred atroom temperature for 30 minutes. This mixture is allowed to age underambient conditions for 48 hours. The final sol is spin coated 700 rpmfor 40 seconds on a 10×10 cm glass sheet followed by thermal curing.

In an embodiment referred to as Example 57, 100 g of sol from Example 56is formulated with 0.2 g of dicumyl peroxide (DCP). The resultingmixture is spin coated at 700 rpm for 40 seconds on a 10×10 cm glasssheet followed by thermal curing.

In an embodiment referred to as Example 58, 100 g of sol from Example 8is formulated with 0.2 g of benzoyl peroxide and 2 g of PGME and 0.8 gof glyoxal. The resulting mixture was spin coated at 700 rpm for 40seconds on a 10×10 cm glass sheet followed by thermal curing.

In an embodiment referred to as Example 59, 100 g of sol from Example 8is formulated with 0.2 g of dicumyl peroxide (DCP) and 1 g of PGME. Theresulting mixture is roll-coated and thermally cured.

In an embodiment referred to as Example 60, 100 g of sol from Example 8is formulated with 0.2 g of dicumyl peroxide (DCP) and 5 g of PGME. Theresulting mixture is roll-coated and thermally cured.

In an embodiment referred to as Example 61, 100 g of sol from Example 8is formulated with 0.3 g of dicumyl peroxide (DCP) and 2 g of PGME. Theresulting mixture is roll-coated and thermally cured.

In an embodiment referred to as Example 62, 100 g of sol from Example 8is formulated with 0.4 g of dicumyl peroxide (DCP) and 2 g of PGME. Theresulting mixture is roll-coated and thermally cured.

In an embodiment referred to as Example 63, 100 g of sol from Example 8is formulated with 0.5 g of dicumyl peroxide (DCP) and 2 g of PGME. Theresulting mixture is roll-coated and thermally cured.

The coatings of the present disclosure also provide tunable mechanicalproperties. Nano-indentation is a method used to measure the mechanicalproperties of nanoscale materials, especially thin films and coatings.The testing instrument that is used for performing the nano-indentationtests is a Nanomechanical Test System (manufactured by Hysitron, Inc.,USA). This Nanomechanical Test System is a high-resolutionnano-mechanical test instrument that performs nano-scale quasi-staticindentation by applying a force to an indenter tip while measuring tipdisplacement into the specimen. During indentation, the applied load andtip displacement are continuously controlled and/or measured, creating aload-displacement curve for each indent. From the load-displacementcurve, nano-hardness and reduced elastic modulus values can bedetermined by applying the Oliver and Pharr method and a pre-calibratedindenter tip area function and a pre-determined machine compliancevalue. The instrument can also provide in situ SPM (scanning probemicroscopy) images of the specimen before and after indentation. Suchnanometer resolution imaging function is accomplished quickly and easilyby utilizing the same tip for imaging as for indentation. The in situSPM imaging capability is not only useful in observing surface features,but also critical in positioning the indenter probe over such featuresfor indentation tests.

Typically nano-hardness and reduced elastic modulus may be determinedusing nano-indentation. The reduced elastic modulus has a relationshipwith the Young's modulus as shown in the equation below. If Poisson'sratio for the material to be tested is known then the Young's modulus offor the material can be calculated. The Poisson's ratio for the diamondindenter is 0.07 and the Young's modulus of the indenter is 1141 GPa.

$\frac{1}{E_{r}} = {\frac{\left( {1 - V_{material}^{2}} \right)}{E_{material}} + \frac{\left( {1 - V_{indenter}^{2}} \right)}{E_{indenter}}}$

The nano-indentation tests were performed on 1 cm² samples cut fromcoated glass specimens made according to the composition of Example 2and Example 3. To obtain the hardness and modulus values for thecoating, ten indents were performed on each sample. Loads of 15 μN wereused for Sample 5F and 25 μN for Sample 7J. All indents were performedthrough in situ SPM imaging. Table 1 summarizes the test conditions andparameters used in the nano-hardness and modulus tests.

TABLE 1 Nano-hardness and Modulus Testing Conditions and ParametersSpecimens Sample 5F and Sample 7J Test instrument TriboIndenterIndentation Load 15, 25 μN Indenter Probe Tip Diamond Berkovich indentertip Temperature 74° F. Humidity 25% RH Environment Ambient air

Tables 2 and 3 present the nano-hardness, H, and reduced elasticmodulus, E_(r), measurement results. These tables also show values forthe contact depth, Hc, of each indent. The test locations of theseindents were chosen to ensure adequate spacing between measurements.

Tables 2 and 3 demonstrate that the average nano-hardness was highestfor Sample 7J (2.11 GPa) and lowest for Sample 5F (1.43 GPa). Averagereduced elastic modulus was highest for Sample 7J (20.99 GPa) and lowestfor Sample 5F (13.51 GPa). These results further confirm that thehardness of the coatings of the disclosure can be tuned by changing theratios of organoalkoxysilane, tetraalkoxysilane andorganofluoroalkoxysilanes in the synthesis of sols from which thecoatings are obtained.

TABLE 2 Nano-hardness and Reduced Elastic Modulus Test Results forSample 5F - Film Made from Composition of Example 2 Test Under H Er Hc15 μN (GPa) (GPa) (nm) 1 1.46 13.93 15.24 2 1.45 13.67 15.16 3 1.4813.38 14.98 4 1.46 13.21 15.13 5 1.48 13.37 15.02 6 1.34 13.50 16.04 71.46 13.55 15.23 8 1.43 13.95 15.40 9 1.43 13.57 15.41 10  1.34 13.0016.06 Average 1.43 13.51 15.37 St. Dev 0.05 0.30 0.39

TABLE 3 Nano-hardness and Reduced Elastic Modulus Test Results for Film7J - Film Made from Composition of Example 3 Test Under H Er Hc 25 μN(GPa) (GPa) (nm) 1 2.09 20.76 15.87 2 2.04 20.75 16.10 3 2.09 20.5315.72 4 2.27 21.75 14.99 5 2.08 21.15 15.82 6 2.13 21.40 15.59 7 2.0920.78 15.80 8 2.03 21.20 16.09 9 2.15 21.22 15.59 10  2.11 20.30 15.78Average 2.11 20.99 15.73 St. Dev 0.07 0.44 0.31

Another series of nano-indentations tests using the conditions of Table4 were carried out for the coating from Example 19 cured under variousconditions.

TABLE 4 Nano-hardness and Modulus Testing Conditions and Parameters.Specimens 6 types of ARC film Test instrument TriboIndenter IndenterProbe Tip Diamond Berkovich indenter tip Indentation Loads 60, 40, 20,17, and 15 μN Temperature 76° F. Humidity 37% RH Environment Ambient air

The cure conditions of coating from Example 19 are summarized in Table5.

TABLE 5 Cure condition for coatings from Example 19: Cure Temp Cure TimeExample 19 (° C.) (min) 19-1A 500 30 19-2A 250 10 19-3A 250 30 19-4A 27510 19-5A 275 30

The results of nano-indentation tests of the coating from Example 19 aresummarized in Tables 6-10.

TABLE 6 Nano-hardness and Reduced Elastic Modulus Test Results for 19-1AH E_(r) H_(c) Test (GPa) (GPa) (nm) 1 1.41 11.06 19.46 2 1.40 11.7019.57 3 1.39 11.18 19.71 4 1.38 11.31 19.78 5 1.37 11.11 19.91 Average1.39 11.27 19.69 S.D. 0.02 0.26 0.18

TABLE 7 Nano-hardness and Reduced Elastic Modulus Test Results for 19-2AH E_(r) H_(c) Test (MPa) (GPa) (nm) 1 560.18 5.76 18.03 2 571.94 6.7617.68 3 515.26 6.26 19.23 4 528.28 6.39 18.84 5 541.52 6.75 18.44Average 543.44 6.38 18.44 S.D. 23.02 0.41 0.62

TABLE 8 Nano-hardness and Reduced Elastic Modulus Test Results for 19-3AH E_(r) H_(c) Test (MPa) (GPa) (nm) 1 534.86 4.09 18.62 2 554.16 4.1618.10 3 531.54 4.15 18.70 4 533.17 4.14 18.68 5 542.68 4.16 18.43Average 539.28 4.14 18.51 S.D. 9.35 0.03 0.25

TABLE 9 Nano-hardness and Reduced Elastic Modulus Test Results for 19-4AH E_(r) H_(c) Test (MPa) (GPa) (nm) 1 533.02 4.12 20.80 2 582.91 4.5019.35 3 572.94 4.53 19.68 4 581.83 4.51 19.44 5 567.28 4.41 19.65Average 567.60 4.41 19.78 S.D. 20.38 0.17 0.58

TABLE 10 Nano-hardness and Reduced Elastic Modulus Test Results for19-5A H E_(r) H_(c) Test (MPa) (GPa) (nm) 1 659.34 5.92 20.08 2 658.886.08 20.12 3 676.19 5.63 19.67 4 677.19 5.63 19.67 5 672.63 5.52 19.72Average 668.85 5.76 19.85 S.D. 9.05 0.23 0.23

The abrasion resistance of the coating is measured by an abrader deviceaccording to European standard EN1096.2 (glass in building, coatedglass). The coatings made according to Examples 1, 2, 3, 4, 5, 6, 7, 8,9, and 10 without any added composition modifying additives, are able tomeet the passing criteria of the standard. Coatings made from Examples3, 7, 8, 9, 10 are exceptional in that they have almost no damage after500 cycles of testing per the EN1096 standard. Abrasion losses are lessthan 0.5%.

The coatings of the present disclosure pass the standard test formeasuring abrasion resistance of coatings on surfaces as definedaccording to European Standard EN1096.2 (Glass in Building, CoatedGlass). The test involves the action of rubbing a felt pad on the coatedglass. The felt rubbing pad is subjected to a to-and-fro translationmotion with a stroke length of 120±5 mm at a speed of 54-66 strokes/mincombined with a continuous rotation of the pad of 6 rpm or of a rotationof between 10° to 30° at the end of each stroke. The back and forthmotion along with the rotation constitutes 1 cycle. The specificationsof the circular felt rubbing pad include a diameter of 14-15 mm,thickness of 10 mm and density of 0.52 g/cm². The felt pad is attachedto a mechanical finger that is 15 mm to 20 mm in diameter and placedunder a load of 4 Newtons. The transmission between 380 nm and 1100 nmis measured to evaluate abrasion resistance and the standard dictates anabsolute change in transmission of no more that 0.5% with respect to areference sample.

TABLE 11 Varying of Abrasion Resistance by Changing the Ratio ofPrecursors on Tin-Sided TCO Glass Pre-Abrasion Post-Abrasion CompositionTransmission Gain Transmission Gain Example 2 2.56 1.69 Example 3 3.172.83 Example7 2.49 2.49 Example 8 2.08 1.83 Example 9 2.69 2.43 Example10 2.06 1.95

The coatings of the present disclosure have abrasion resistance that canbe tuned or modulated in a variety of ways. Examples in Table 11demonstrate how the abrasion resistance of the coatings from thisdisclosure can be tuned or modulated by changing sol composition fromwhich the coatings are obtained. It would be beneficial to be able toprovide coatings as in Example 3 that have a higher durability againstabrasion for solar modules or glass substrates that are exposed toabrasive natural environments like sandstorms or cleaning actions thatinvolve contacting the antireflective coatings with abrasives. In areaswhere the solar modules are unlikely to be exposed to significantabrasive environments, it might be more beneficial to provide coatingsthat have a higher pre-abrasion transmission as in Example 2.

The contact angle of the coatings is measured by means of a goniometerwherein the contact angle of the water droplet is measured by means of aCCD camera. An average of three measurements is used for each sample. Ontin-sided float glass, average contact angles for coatings made fromExamples 2, 4, 5 and 6 measure 85° and on tin-sided TCO glass, averagecontact angles measure 90°.

The reliability results of the coatings in this disclosure are broadlysimilar to existing anti-reflective coatings. However, under 85° C./85%RH test conditions per IEC61215 and IEC61646, the coatings of thisdisclosure have a protective effect on glass corrosion which is notobserved when highly porous anti-reflective sol-gel coatings are testedunder similar conditions. Without being bound to theory, we believe thatporous anti-reflective coatings facilitate easy leaching of sodium ionsfrom the glass, whereas the coatings of this disclosure can be tuned toachieve hydrophobic properties which slow down the rate and/or decreasethe amount of water that is in contact with the glass. Coatings madefrom examples 2, 4, 5 and 6 of this disclosure exhibit minimal glasscorrosion compared to uncoated glass. The other remarkable feature isthat these reliability results have been achieved with a coating curedat just 120° C. Existing anti-reflective coatings are typically sinteredat 400˜700° C. to achieve the level of reliability indicated by theseresults.

Where applicable, the measurement of anti-reflective properties of thecoatings is done as follows: the transmittance of the coatings ismeasured by means of UV-vis spectrophotometer equipped with anintegrator accessory. The anti-reflective enhancement factor is measuredas the relative percent increase in transmittance compared to untreatedglass slides versus glass slides coated with compositions of thisdisclosure. ASTM E424 describes the solar transmission gain, which isdefined as the relative percent difference in transmission of solarradiation before and after the application of the coating. The coatingsexhibit about 1.5% to about 3.25% gain in solar transmission. Therefractive index of the coating is measured by an ellipsometer.

Coated samples of Examples 11-63 were cured at various conditions. Filmthickness, refractive index (RI), solar weighted transmission delta(ΔT_(AM)), and abrasion performance according to tests described hereinbased on European Standard EN1096.2 (Glass in Building, Coated Glass)were measured and summarized in Table 11a.

The T_(AM) metric is solar-weighted transmission using the ISO60904solar spectrum between 380 nm to 1100 nm. ΔT_(AM) is the absolutedifference T_(AM) between a coated sample of glass and an uncoatedsample of the same type of glass.

TABLE 11a Cure conditions, metrology and performance results of coatingsfrom examples. Cure Cure Example Temperature Time Thickness Abrasion #(° C.) (min) (nm) RI ΔT_(AM) P/F 11 500 30 135.30 1.258 3.22 P 12 500 30120.40 1.289 2.99 P 13 500 30 126.20 1.325 2.75 P 14 500 30 120.53 1.2603.34 P 14 Tempered 124.43 1.280 3.04 P 16 500 30 127.30 1.260 3.23 P 17500 30 103.70 1.290 2.84 P 18 300 60 131.09 1.340 2.56 P 19 500 30129.33 1.280 3.07 P 20 300 30 142.90 1.340 2.45 F 21 300 30 154.80 1.2902.76 P 22 550 15 147.10 1.260 3.14 P 23 550 15 121.63 1.290 2.98 P 24550 15 133.20 1.270 3.18 P 25 300 30 136.27 1.360 2.13 F 26 300 30162.10 1.313 2.49 F 27 300 15 133.85 1.288 2.91 F 28 300 15 124.13 1.2903.00 F 29 300 15 130.00 1.311 2.89 P 30 300 15 135.97 1.316 2.91 P 31300 30 127.30 1.341 2.50 — 32 550 15 89.20 1.383 1.48 P 33 300 30 105.231.387 1.80 P 34 550 15 125.78 1.307 3.05 — 35 300 15 120.53 1.37 1.95 P36 275 30 100.32 1.38 1.88 P 39 275 30 120.50 1.36 2.25 P 42 275 30106.86 1.38 2.17 P 44 275 30 104.48 1.34 2.28 P 45 275 30 106.86 1.382.17 P 46 275 30 110.86 1.35 2.52 P 47 275 30 129.98 1.36 2.69 P 48 27530 117.48 1.36 2.33 P 49 275 30 119.78 1.36 2.47 P 50 275 30 117.46 1.352.50 P 51 275 30 123.66 1.36 2.53 P 52 275 30 103.66 1.40 2.01 P 53 27530 123.30 1.35 2.45 P 54 800 30 sec 112.78 1.39 1.88 P 55 800 40 sec118.02 1.35 2.54 P 56 275 30 105.92 1.38 1.88 P 57 275 30 127.06 1.362.24 P 58 275 30 126.28 1.35 2.45 P 59 275 30 121.00 1.39 2.18 — 60 27530 117.00 1.38 2.29 — 61 275 30 129.00 1.38 2.34 — 62 275 30 123.00 1.332.92 — 63 275 30 120.00 1.31 3.08 —

Embodiments of the invention have ΔT_(AM) in the range of between about1.4% to about 3.5% and between about 1.5% to about 3.25% and betweenabout 2.0% to about 3% and greater than about 1.5%. Embodiments haverefractive indices of between about 1.25 to about 1.45 and between about1.30 to about 1.42 and between about 1.35 to about 1.40.

FIG. 1 a illustrates the UV-vis transmittance spectra showing maximumtransmittance enhancement of coatings on tin side of float glass fromcomposition given in Example 2. A statistical comparison of 11 samplesfrom coating made from composition in Example 2 on tin side vs non-tinside of float glass provided a solar weighted photon gain of 2.23% vs1.93%. Without being bound to theory, the coatings of this disclosureinteract with the tin side of float glass to provide an enhancement inthe beneficial properties of the antireflective coatings.

FIG. 1 b illustrates the UV-vis transmittance spectra of roll-coatedcoating made from Example 3 on a patterned glass substrate.

FIG. 2 a illustrates the UV-vis transmittance spectra showing maximumtransmittance enhancement of coatings on tin side of TCO glasssubstrates made from compositions given in Example 3 comparing pre- andpost-abrasion spectra.

FIGS. 2 b and 2 c illustrate the UV-vis transmittance spectra ofcoatings made from example 5 and Sols from the three formulations couldhave different inherent viscosities and it would be preferable to beable to tune the viscosities of the sols such that their solar-weightedphoton gain is maximized.

FIG. 3 a is a TEM cross-sectional view of a coating made from thecomposition of Example 2 on a glass slide substrate. The TEM images showthe absence of any discernible porosity in these coatings. The filmthickness about 70-80 nm.

FIG. 3 b is a HRTEM of a coating made from the composition of Example 2on a glass slide.

FIG. 4 is an SEM cross-sectional view of a coating made from thecomposition of Example 2 on a 30×30 cm float glass substrate. The SEMimages show the absence of porosity and a film thickness of 133 nm.

FIG. 5 is an SEM cross-sectional view of a coating made from thecomposition of Example 3 on a 30×30 cm float glass substrate. The SEMimages show the absence of porosity and a film thickness of ˜83 nm.

FIG. 6 is an SEM cross-sectional view of a coating made from thecomposition of Example 4 on a 30×30 cm float glass substrate. The SEMimages show the absence of porosity and a film thickness of 76 nm.

It should be appreciated that in some embodiments, the coatings of thepresent disclosure provide an increase in transmission from about 1% toabout 3.5% and in some embodiments from about 1.5% to about 3%, and acontact angle of about 80 degrees to about 120 degrees and in someembodiments about 85 degrees to about 100 degrees.

Typical hardness for a mixture of pure silica sol-gels coatings isobserved to be around 1.05 GPa. Without wishing to be bound by theory,the enhanced mechanical properties of some of the coatings of thisdisclosure (as compared to pure silica-based coatings) may be due toseveral factors that contribute to increased hardness. First, theextensive cross-linking due to the use of the three-precursor systemmakes the Si—O—Si network stronger. Second, the combined use oforganosiloxane and organofluorosiloxane enhances the noncovalentinteractions between the organic side chains to promote betterinteractions that enhance the overall mechanical properties. Third, theincreased interactions between the side chains promote a better fillingof porous void space in the sol-gel network to make a homogenous andlargely nonporous coating. Taken together, the unique combination ofprecursors along with the absence of visible porous microstructure andthe enhanced side chain interactions between the organic groups providesthe improved mechanical properties as compared to coatings of the priorart.

The anti-soiling and self-cleaning property of coatings of thisdisclosure can be tuned by changing the surface characteristics of thesecoatings. XPS data for coatings of this disclosure show how the fluorinecontent of the coatings can be varied from 0-9.1% and carbon content canbe varied from 16.8% to 41.7%.

TABLE 12 XPS Data for Coatings of this Disclosure on Tin Side of TCOCoated Glass Subject to 20 sec Ar+ sputter to remove any adventitiousimpurities Sample F % C % Si % O % N % Na % Ca % Example 2 + 20 sec 9.141.7 16.1 32.1 nd 0.6 0.4 sputter Example 3 + 20 sec nd 16.8 28.5 53.6nd 0.7 0.3 sputter Example 4 + 20 sec 7.4 25.3 21.7 44.1 0.5 1.0 ndsputter

TABLE 13 XPS Data for Coatings of this Disclosure in the native stateand after 10 minutes of Argon Sputter Etch on Tin Side of TCO coatedGlass Sample F % C % Si % O % Sn % Na % Ca % Example 2 as 11.9 39.5 14.932.7 nd 0.6 0.4 received Example 2 after 10 12.9 13.1 28.7 45.1 0.2 Ndnd min sputter

A comparison of the XPS data for the as-received sample from Example 2and the XPS data for the same sample after it is sputtered with Argonions for 10 minutes show that fluorine from the coating material ispresent in the as-received sample and after the 10 minute etch. The dataalso shows that a small amount of tin from the tin side of the TCOcoated float glass is detected along with the coating.

As indicated elsewhere herein, the coatings of this disclosure may bedeposited on substrates by techniques known in the art, including dipcoating, spraying, drop rolling, or flow coating to form a uniformcoating on the substrate. A flow coating head, as depicted in FIG. 9,FIG. 10, FIG. 11, FIG. 12, FIG. 13, and FIG. 14 may enable improvementsin flow coating. A process for roll coating is described in FIG. 15A,FIG. 15B, and FIG. 16.

FIG. 9 depicts an embodiment of laboratory scale flow coating. Inembodiments, a nozzle (101) dispenses a material (102) onto an inclinedsubstrate (103) as it is moved across the top edge of the substrate. Thematerial flows down the substrate, and the excess drips from the bottomedge of the substrate. The material that remains adhered to thesubstrate undergoes a gelation process as it dries and forms a thin-filmcoating on the substrate.

While the basic laboratory system shown in FIG. 9 can be scaled up insubstrate size, its rate of coating may be slow and wasteful of coatingmaterial. It is possible to recover the coating material that drips offthe bottom edge and recycle it to the nozzle, but this makes control ofcomposition and contamination of the recycled material difficult. Whatis needed is a flow coating system that has a fast coating rate and thatis economical with coating material with minimal wastage dripping fromthe bottom edge, without recycling of this material.

In one embodiment, a coating head such as the one shown in FIG. 13 andin cross-section in FIG. 10 may be used in flow coating. The coatinghead includes a long slot (116) formed between a lower slot manifold(110) and an upper slot manifold (111). This slot is positioned parallelto and extends along the length of the top edge of an inclined substrate(120). In an embodiment, the slot is approximately as long as the edgeof the substrate to be coated. For example, the slot may be orientedalong the longer edge of a rectangular substrate, such that the fluidflows down the substrate along its shorter edge. This orientationminimizes the time required for gravity to carry the fluid across theentire area of the substrate. In an embodiment, a distribution blade(112) bridges the gap between the slot and the top edge of the substratesuch that coating material flowing out of the slot is deposited on tothe distribution blade and then flows under gravity to the bottom of thedistribution blade, which contacts the front surface of the substratejust below the top edge of the substrate. The coating material thenflows off the distribution blade onto the front surface of the substrateand from there down the substrate until eventually it either drips fromthe bottom edge or is removed by other means. The length of thedistribution blade is slightly longer than the length of the slot and ofthe edge of the substrate that is being coated. In an embodiment, thedistribution blade extends beyond each end of the slot manifoldassemblies. For example, the distribution blade may extend 2-100 mmbeyond each end of the slot manifold assemblies. In another example, thedistribution blade may extend 10 mm beyond the substrate.

Coating material is supplied to the slot by a dispensing system, such asa pump (not shown) capable of transferring the liquid coating material,and that is also capable of delivering a measured quantity of coatingmaterial through one or more inlet ports (113) in the lower slotmanifold. The inlet port directs material into a corresponding internalpocket (114) within the lower slot manifold that allows the coatingmaterial to accumulate below the lip of the slot and to spread evenlyalong the slot before it begins to overflow the slot and flow onto thedistribution blade, providing a uniform fluid front of material over theblade. FIG. 12 shows an isometric view of the internal detail of a lowerslot manifold (110). The coating material flows from the port inlet,located in the middle of the internal pocket, outwards toward the endsof the internal pocket and so is distributed evenly along the back sideof the slot lip (140). Once enough material has filled the internalpocket it will begin to overflow the slot lip evenly along the length ofthe slot. The upper slot manifold (not shown in FIG. 12) forms theopposing side of the slot. A seal channel (141) may allow the assemblyto close to the appropriate slot width, as is described herein.

Producing high quality coatings of uniform thickness onto the substratemay depend on the rate at which the fluid flows through the slot. Inturn, the rate at which the material flows may be highly dependent uponseveral factors of the design including the slot length (l), width (w)(152) and height (h) (151), as seen in FIG. 14, the viscosity (p) anddensity (p) of the coating material, and the pressure differential (ΔP)over the width of the slot. In an embodiment, the fluid flow in the slotis both laminar and has a fully developed velocity profile upon exitonto the distribution blade. Laminar flow in the slot can be achieved byensuring the fluid has a Reynolds number less than 1,400. In anembodiment, the Reynolds number (Re) of the coating fluid within theslot is less than 100. The coating fluid may exit the slot with avelocity profile that is independent of subtle edge effects, turbulenceand other disturbances present at the coating fluid's entry into theslot. This condition can be achieved by ensuring the width of the slotis significantly longer than the flow's characteristic entrance length(Le). In an embodiment, the slot width is equal to at least 10 times theentrance length. Such a condition is governed in the following relation,which uses the Blasius approximation to solve for the entrance lengthbetween parallel surfaces:

$L_{e} = \frac{{hRe}_{h}}{100}$

The volumetric rate at which the coating fluid flows through the slot isclosely approximated by the following relation:

$Q = \frac{l\; \Delta \; {Ph}^{3}}{12\; w\; \mu}$

With average flow speed, V, determined by:

$V = \frac{Q}{lh}$

In an embodiment, sol coating flow rates per unit slot length of between5×10⁻⁹ and 5×10⁻⁴ m²/s are useful for coating glass substrates of highquality, and uniform thickness. In an embodiment with a 2 meter longslot, this equates to a volumetric flow rate between 1×10⁻⁷ and 1×10⁻³m³/s. To prevent splatter or turbulent flow or other undesirablephenomena from impacting the distribution blade or substrate, coatingmaterial may not be forced from the slot under high pressure or flowrates. For example, gravity force may be used to drive fluid from theinternal pocket to the distribution blade. In an embodiment, the slot isdesigned such that for the chosen coating material properties, the flowrate out of the slot is less than the flow rate into the internalpocket. This has the effect of building a reservoir of coating materialbehind the slot in the internal pocket, forcing it to spread evenlyunder the influence of gravity along the entire length of the slot andto build up a head height H (150), as in FIG. 14, inside the internalpocket. If the flow rate through the slot is too high, then coatingmaterial will completely flow through part of the slot before spreadingalong the entire length of the slot and reaching the ends furthest awayfrom the inlet port. If the flow rate is too low, then the internalpocket may completely fill with coating material causing an increase inpressure that will create uneven flow rates and excessive back pressureon the coating fluid, and adversely affect the flow rate through theslot. All of these issues can cause the slot flow rate to vary and canaffect the quality and uniformity of the coating. The pressure drop overthe slot width, ΔP, can be related the fluid head height within theinterior pocket, H (150), the internal pocket pressure Po (154),pressure at the entrance to the narrow slot, P1 (153), and the pressureat the exit of the slot, P2 (155), the fluid material density ρ and thegravitational constant g according to the following relationship:

ΔP=P ₁ −P ₂

ΔP=ρgH+P _(o)

This pressure input as a function of head height, combined with thedesired flow rate drives the desired slot height, h (151). As a result,careful consideration should be paid to the pressure in the internalpocket. Some embodiments keep the internal pocket sealed via a gasket,o-ring or sealant such that pressure is controlled by the relative flowrates of coating material into and out of the pocket. Other embodimentsmay include vents between the internal pocket and ambient pressure or toan auxiliary pressurization system. In an embodiment, pressure insidethe pocket is vented to the atmosphere and slot height, h, is determinedby the following relationship:

$h = \sqrt[3]{\frac{12\; {Qw}\; \mu}{l\; \rho \; \; H}}$

Given the above parameters, for a typical sol coating, the width of theslot is between 0.05 and 2 mm, and preferably 0.1 to 0.5 mm. This widthmay be controlled by placing shims between the upper and lower slotmanifolds. Alternative embodiments may use machined steps or other gapcontrol methods. The assembly of upper and lower slot manifolds may havea gasket-like seal along the top and sides to ensure material isdirected towards the slot. An O-ring or similar internal pocket seal mayallow the assembly to close to the appropriate slot width, and may befacilitated with the use of a seal channel (141).

The distribution blade may serve at least three functions in enablingconsistent and uniform coating thickness; 1) it provides a path forcoating material to flow from the slot to the substrate; 2) it has ahigh energy surface that causes the material to spread evenly by surfacetension during its travel from the slot to the substrate; and 3) itprovides an interface to the substrate surface that is tolerant ofimperfections in flatness or warping of the substrate. In oneembodiment, the distribution blade is relatively more flexible than thesubstrate and is able to conform to an uneven or warped substrate. Forexample, the distribution blade is 316L stainless steel, 2020 mm long,45 mm wide and 0.38 mm thick and the substrate is tempered soda-limeglass 1970 mm long, 984 mm wide and 3.2 mm thick. In another embodiment,the distribution blade is relatively more rigid than the substrate and amechanism clamps the substrate to the back surface such that it is heldflat against the distribution blade. In one embodiment, the distributionblade has a surface energy between 25 mN/m and 100 mN/m.

The coating material exiting the head slot may not naturally form acontinuous curtain or “waterfall” of coating material in the absence ofthe distribution blade, and instead, the coating material may exit theslot with many drips or small rivulets of material all along the lengthof the slot which may not result in a consistent or uniform thicknesscoating on the substrate. To achieve a curtain or “waterfall” out of theslot head in the absence of the distribution blade would requiresignificantly greater flow rates of coating material, and couldtherefore result in significant waste of coating material. Thus, thedistribution blade enables a consistent and uniform thickness coatingwith minimal material waste.

In FIG. 10, the distribution blade is a thin piece of material that isheld in place by a backing plate (118) that along with the distributionblade is attached to the upper slot manifold (111) by a plurality ofbolts or other fastening means (119). This backing plate also serves totension the distribution blade by forcing it forward at a slight angle.This reduces warping of the thin distribution blade along its length.The upper and lower slot manifolds are held together by a plurality ofbolts or other fastening means (117). In some embodiments the bottomedge of the thin distribution blade may be beveled or rounded. In apreferred embodiment it is beveled between 15° and 60°.

In some embodiments the distribution blade is made from a stainlesssteel alloy such as 316L. In other embodiments it could be made fromtitanium, chrome or nickel plated steel, various corrosion resistantalloys, glass, ceramics, polymer or composite materials such as a metalcoated polymer. The material may be chosen to be chemically resistant tothe composition of the coating material such that it is not damaged bythe coating material and such that it does not contaminate the coatingmaterial in any way.

In FIG. 10, the lower slot manifold has a notch (115) just below theslot. The purpose of this notch is to prevent the flow of coatingmaterial from the slot along the bottom edge of the lower slot manifoldand from there dripping on to the distribution blade or the substrate.

FIG. 11 shows an alternative embodiment of a distribution blade (130)wherein the blade is a solid piece of material that also forms the upperslot manifold. The front surface of the blade (132) acts to distributethe coating material evenly from the slot to the substrate. The bottomedge of the blade is profiled (133) to facilitate the flow of coatingmaterial from the blade onto the substrate. It should be understood thatthe exact shape of this profile can include curved or angled flat bevelsand that the transition of angle from the face of the distribution bladecan range from gradual to abrupt and that the final angle that the edgemakes with the substrate surface can be from 10° (sharp) to 110° degrees(obtuse). In another embodiment, the thick or solid distribution bladedoes not also form the upper slot manifold, but is instead a separatepiece that is bolted onto the slot manifold in a manner similar to thethin distribution blade shown in FIG. 10.

Some embodiments of the distribution blade include coatings or surfacetreatments on the front side (that is the wet side) and on the backside. For example, a front side surface treatment may enhance thespreading of the coating material as it flows to the substrate. Aback-side treatment might repel the coating material to suppressmaterial gathering on the backside due to capillary action that thendripped onto the substrate as it was removed from the distribution orgather on the backside and contaminate the next substrate positionedagainst the blade. Other embodiments of the distribution blade includelaminates and composites where dissimilar materials are fused orassembled together to provide differences between the front and backsidesurface properties as might also be achieved in the case of a coatedmetal blade.

Some embodiments of the coating head manifolds may have coatings orsurface treatments to protect them from adverse chemical reactions withthe coating material or to change how the coating material flows withinthe internal pocket or over the slot lip.

A full coating head may be composed of a plurality of slot manifoldassemblies. For example each slot manifold assembly might be 50 cm long.Four such assemblies may be mounted on a supporting structure such thatthey form a 200 cm long coating head. The dimensions of the slotmanifold assembly and the number of such assemblies used for aparticular length of coating head may be selected to manage the cost ofmanufacturing the slot manifolds themselves and the complexity ofconstructing the coating head from multiple slot manifold assemblies. Inthe case where multiple slot manifold assemblies are used to assemble acoating head, it is advantageous to have a single distribution bladethat is continuous over the entire length of the coating head. However,multiple adjacent or overlapping segments of distribution bladecomprising the length of the coating head are not precluded.

It should be understood that the number of internal pockets and inletports within a slot manifold is variable and may be more or less thanthe two shown in FIG. 12. The number of pockets and inlet ports may beselected to manage the manufacturing complexity of the slot manifold andthe uniformity of flow of coating material from the slot.

In the slot manifold, the wall between internal pockets may be kept asthin as possible. This wall affects the flow of material over the slotlip in its immediate vicinity. By keeping the wall as thin as ispractical, the effect is minimized.

The method of coating using the apparatus may include the followingsteps. First, optionally, the substrate may be prepared for the coatingby increasing the surface energy of the surface to be coated, thusmaking it possible for the coating material to spread evenly on thesubstrate surface by surface tension. In one embodiment, the substrateis glass and the surface energy is increased by washing vigorously withwater and/or mechanical brushes. In other embodiments, the substratesurface may be prepared using gas plasma such as oxygen or by treatmentwith a gas flame. Other pretreatments are described further herein.

Next, the substrate to be coated may be positioned with its top edgealigned with and parallel to the bottom edge of the distribution blade.The bottom edge of the distribution blade may overlap slightly with thetop edge of the substrate. The amount of overlap is dependent upon thecoating requirements but may be at least 0.1 mm and in a preferredembodiment be approximately 3 mm. The ends of the distribution blade mayextend slightly beyond the left and right edges of the substrate,between 2 and 100 mm on each side. In an embodiment, it extends by 10 mmon each side. The substrate may be inclined at an angle of 60° to 85°relative to horizontal. In the case of a flexible thin distributionblade, the angle between the surface of the substrate and the surface ofthe distribution blade may be between 0° and 5°. The substrate can bepushed slightly against the distribution blade to apply pressure to thecontact area such that the distribution blade conforms to any grossirregularity or deviation from flatness of the substrate. In the case ofa rigid distribution blade, the substrate may be positioned with itsfront surface parallel to the back surface of the distribution blade anda clamping mechanism may hold the substrate to the distribution bladesuch that any warping or deviation from flatness of the substrate iseliminated against the flat back side of the distribution blade. In oneembodiment, the coating head is stationary and the substrate is broughtto it. However, in other embodiments, the substrate may be stationaryand the coating head moved to position or both elements may movetogether to arrive at the final coating position. It is also possiblefor both elements to be stationary relative to each other but to bemoving relative to the larger coating system.

Next, the front surface of the substrate may be completely wetted with apre-wet solution. This pre-wet solution is dispensed in a manner thatquickly wets the entire substrate surface rapidly, such as in less than30 seconds. In one embodiment, a plurality of fan nozzles positioned ona rotatable mechanism above and in front of the substrate and along itslength aligned to the coating head starts spraying pre-wet solution suchthat it first wets the distribution blade along it entire length. Thenthe nozzle assembly rotates such that the fan shaped jets of pre-wetsolution from the nozzles travel down the substrate from its top edge toits bottom edge and in the process deposit pre-wet solution on the fullsurface of the distribution blade and the substrate. When employed, thepre-wet step decreases the time for the coating material to completelywet the substrate to between 1 and 25 seconds; improves the uniformityof distribution of the coating material on the substrate to ±25% byvolume per unit area and reduces the amount of coating material neededto completely coat the substrate by up to 90%. The composition of thepre-wet solution is chosen to provide a number of properties: Theviscosity is within ±50% of the viscosity of the coating material andmore preferably within ±10% and even more preferably within ±2% and/orthe surface tension is within ±50% of the surface tension of the coatingmaterial and more preferably within ±10% and even more preferably within±2% and/or the vapor pressure is within ±50% of the vapor pressure ofthe coating material and more preferably within ±10% and even morepreferably within ±2%. In one embodiment, the pre-wet solution comprisesthe same mixture of solvents, mixed in the same ratios as the coatingmaterial. For example, the pre-wet solution might be composed of 90%isopropyl alcohol and 10% water that approximately matches the ratio ofisopropyl alcohol and water in a sol-gel coating material. In analternative embodiment, the pre-wet solution could be a non-ionic,cationic or anionic surfactant, such as for example sodium dodecylsulfate or perfluoroalkyl sulfonate.

Next or some time shortly after the pre-wet step has commenced, apre-determined amount of coating material may be dispensed from thecoating head on to the substrate. The coating material flows down thesubstrate completely covering the front surface of the substrate. Excesscoating material may drip from the bottom edge or be wicked away frombottom edge by capillary action onto a mechanism designed for thatpurpose. In some embodiments, excess coating material may be collectedat the bottom of the substrate for reuse. The decision to reuse thismaterial or not depends on the composition of the coating material andsubstrate. For example, if the coating material is quite stable and doesnot significantly change during the time it travels down the substrateand if the substrate does not contaminate the coating material then adecision might be made to reuse excess material collected from thebottom edge.

Next, optionally, there may be a pause of between 1 and 600 secondsafter the dispensing of coating material has finished while excesscoating material is able to drain out of the internal pocket and fromthe wet surface of the distribution blade onto the substrate. The lengthof this pause may be optimized to reduce the possibility of drips fromthe distribution blade after the substrate is removed from the coatinghead. In some embodiments, this pause may be long enough to allow thedistribution blade and/or the top area of the substrate to dry orpartially dry.

Next, the substrate may be withdrawn from the coating head. In someembodiments, if the coating head is still wet, a drip guard may quicklymove into place between the substrate and the bottom edge of thedistribution blade. This drip guard may optionally touch the bottom edgeof the blade to wick away excess material in which case the surface ofthe drip guard may have similar surface characteristics to the frontsurface of the distribution blade to encourage the coating material toeasily flow off the distribution blade.

Finally, the substrate may be allowed to dry in a manner that allows thecoating material to undergo gelation such that a uniform high qualitycoating is formed on the substrate surface.

This coating method, enabled by the novel design of the coating head canhave several of the following advantages over alternative coatingtechniques. First, by dispensing material simultaneously across the fullwidth of the substrate the time to dispense can be greatly shortened.Second, by pre-wetting the substrate the amount of time for the coatingmaterial to flow down the substrate can be greatly shortened and theamount of coating material required to fully wet the substrate surfaceis greatly reduced. Third, if coating material is not collected at thebottom of the substrate for reuse then only fresh (virgin) material canbe deposited on the substrate so control of coating material purity andcomposition can be greatly increased. Fourth, by utilizing adistribution blade in conjunction with a properly sized slot dispenser,the uniformity of flow of material on to the substrate can be greatlyincreased at very low cost and with a very simply system. Fifth, thetechnique can be very tolerant of deviation of flatness on the substratewithout requiring any precision mechanical control or design. Sixth, themethod does not necessarily pose any significant chemical compatibilitychallenges where it may be difficult to identify critical coatingcomponents with properties that are not sensitive to or contaminate thecoating material. Finally, the method can be inherently single sidedallowing the flexibility to coat one side of the substrate or both (in asecond coating step) if needed.

Is should also be understood that in some embodiments the formulation ofthe coating material will have a significant effect on the uniformity ofthe thin-film. In particular, in a sol-gel coating material the ratio ofsolids or particle content to solvent in conjunction with the ambientconditions during drying may affect the gelation process that occurs asthe thin-film forms. Careful control of these elements will enhance theuniformity of the final thin-film especially in the top to bottomdirection on the substrate.

FIG. 15 a shows a simplified schematic of a forward roll coatingapparatus. FIG. 15 b shows a simplified schematic of a reverseroll-coating apparatus. In both figures, a flat substrate (160) is fedfrom left to right. A counter pressure roller (163) supports thesubstrate from the bottom and moves in a complementary direction to themovement of the substrate. A coating material (164) is deposited in areservoir created between a doctor roller (162) and an applicationroller (161). The pressure or spacing of the doctor roller toapplication roller controls the amount of coating material that istransferred to the application roller. The surfaces of the doctor andapplication rollers may be smooth or textured, soft or hard. The rollersurfaces need not be the same. For example, the doctor roller may becompliant and textured while the application roller could be hard andsmooth and vice versa. The application roller transfers coating materialto the surface of the substrate. The pressure or distance between theapplication roller and the substrate surface is adjustable to facilitatecontrol of the final wet-coating thickness and/or uniformity of thematerial on the substrate. In forward roll-coating, the applicationroller (161) moves in the same direction as the direction of motion ofthe substrate. In reverse roll-coating, the application roller (161)moves in the opposite direction to the motion of the substrate.

The substrate may be continuous, such as for example a roll of polymersheet or steel, or it may be discontinuous, such as discrete pieces ofglass or wood or individual solar modules. In the case of discontinuoussubstrates, the application roller assembly may be moved in a verticaldirection such that it touches down on the leading edge of the substrateas it enters the roll-coater and then lifts off the trailing edge as thesubstrate exits the roll-coater. This technique may reduce uniformity onthe leading and trailing edges.

The selection of the materials within the roll-coater that come intocontact with the liquid coating material are a consideration. In someembodiments, the coating material may be corrosive, having either a highor low pH. In an embodiment, the pH of the coating material is between1.8 and 2.8. Additionally, in some embodiments, the coating materialcontains organic solvents such as iso-propyl alcohol, methanol, ethanol,propanol, propylene glycol monomethyl ether (PGME), propylene glycolmonomethyl ether acetate, and the like. All materials may be selected towithstand both the organic solvents and pH conditions used. For metalliccomponents, stainless steel is preferential with chrome-plated steel,for example. In selecting polymer materials for pipes, fittings andseals made from polytetrafluoroethylene, polypropylene, polyether etherketone, and polyvinylidene difluoride may be considered. For polymercoatings on the rollers polyurethane, EPDM (ethylene propylene dienemonomer) rubber and nitrile rubber are suitable. The particularembodiment of a roll-coater selected for a specific sol-gel coatingapplication depends upon a number of factors. The wet film thickness isa process parameter to consider in achieving the final cured filmthickness. The desired wet thickness may be dependent on the desiredfinal dry thickness, the solids content of the coating material and thetarget porosity of the final dry film. In one embodiment, the desiredfinal thickness is 120 nm (DT), the solids content (SC) of the coatingmaterial is between 1% and 3% by volume and the target porosity (P) is10%. The target wet thickness (WT) may be calculated with the followingformula:

${W\; T} = \frac{D\; T}{{SC}*\left( {1 - P} \right)}$

For example, the equation yields a target wet thickness betweenapproximately 4 μm and 14 μm using the input parameters above. Wetthickness can be controlled by a number of process controls on theroll-coater system. Selection of which parameters are most important isdependent upon the characteristics of the coating material, such as forexample its viscosity, and the architecture or operation mode of theroll-coater, such as forward or reverse. Typically, the parametersadjusted are the doctor roller spacing and/or pressure to theapplication roller; the application roller spacing/pressure to thesubstrate; the speed at which the substrate moves and in the case ofreverse roll-coating the difference in speed between the substrate andthe application roller. The speed at which the doctor roller movesrelative to the application roller is also a process parameter. FIG. 16shows an embodiment of a roll-coater used for sol-gel coating of flatsubstrates such as glass or solar modules. The roll-coater (170) ispositioned after a feed-in conveyor (171) and ahead of a feed-outconveyor (172). In FIG. 16, substrates move from right to left. Coatingmaterial (173) is fed to the roll-coater from a storage tank at acontrolled rate by a pump (174). Excess material is collected (177) offthe ends of the rollers and recirculated. An optional pre-heater (175)may be positioned such that it can heat the substrate prior to theroll-coater. The substrate may be heated to a temperature between about2° C. to about 80° C. and between about 20° C. to about 50° C. andbetween about 30° C. to about 40° C. In some embodiments this pre-heatstep may be used to reduce thermal stress during the very rapid heatingof subsequent process step. In some embodiments the pre-heat step may beused to achieve specific coating process targets such as uniformity,thickness, porosity, pore-size, pore-morphology, pore-distribution inthe coating, pore-size distribution and process speed. Carefulconsideration should be paid regarding heat transfer from warmedsubstrates to the application roller such that it is accounted for inthe process. In some embodiments a flash-off heater (176) is positionedat the output of the roll-coater to control evaporation of the solventof the coating material to facilitate the gelation of the thin-film. Insome embodiments the coating material may be heated to a temperature ofbetween about 25° C. to about 60° C. and between about 30° C. to about50° C. In some embodiments, the pre-heater and the flash-off heater maybe radiant infra-red or they may be electric or fuel fired convectionheaters or a combination or the like. In some embodiments forced air atambient or close to ambient temperature could be used to accomplish theflash-off process by accelerating solvent evaporation.

The conveyor systems used to move substrates between process stages maybe continuous belt driven systems. In some embodiments robots might beused to convey substrates between process stages. In other embodimentsubstrates might be conveyed by humans using carts. In any case itshould be understood that substrates may be conveyed between processsteps by many means known in the art.

An important consideration when using roll-coaters is accommodating orcontrolling for evaporation of coating material solvent from theequipment itself as the machine is running To mitigate this evaporation,it can be advantageous to add make-up solvent to the coating materialsuch that the solids concentration is controlled within a workablerange. Make-up solvent can be added at a constant rate known to matchthe steady-state rate of evaporation; it can be added periodically basedon pre-determined intervals based on time, quantities of substratescoated, or coating material consumed. Make-up solvent can be added basedon an active feedback loop wherein the solids concentration is measureddirectly or indirectly and then used to control the amount added. Solidsconcentration might be measured by optical means such as dynamic lightscattering or adsorption or refractive index; it could be measured byphysical properties such as for example density or viscosity; it couldbe measured chemically such as for example monitoring pH.

Sol-gel materials used for coatings are often sensitive to environmentalconditions such as relative humidity and temperature during the gelationprocess. Additionally, sol-gel materials may release significant amountsof solvent vapor prior to or during cure. It is therefore desirable toengineer the environment around the roll-coating system such as thattemperature and humidity are controlled, and solvent vapor is removed.In some embodiments a containment chamber is built around the completeroll-coater system with a dedicated HVAC unit to control temperature andrelative humidity. In an embodiment, there is a secondary interiorcontainment around the coater application roller and the flash-off areathat is small in volume such that its temperature and relative humiditycan be controlled more easily. This interior containment area is alsoused to collect solvent vapor for venting, destruction or recycling.This has an additional advantage to prevent people working inside theprimary containment area from being subjected to elevated levels ofsolvent vapor. Such an environmental chamber system would have safetyinterlocks such that the tool could be stopped and any coating materialsafely contained if the solvent vapors approached flammability safetylimits.

FIG. 17 shows a cross-sectional schematic view of one embodiment of acuring apparatus and method for skin-cure. In this apparatus, anair-knife (180) directs heated air on to the surface of a substrate(181) presented to the air-knife by a feed-in conveyor (182) andextracted by a feed-out conveyor (183). The air may be heated by anelectrical element (184), as shown in FIG. 17, may also be heated by anyother method known in the art. The air may be heated to any temperatureuseful in the method, such as to a temperature of 300° C. to 1000° C.Air may be forced through the heating element and air-knife by a fan(185). The temperature of the air is controlled by an electroniccontroller (186) and temperature sensor (188) located in the heated airstream. Optionally, overheat protection of the heating element may beprovided by the electronic controller and, optionally, a secondtemperature sensor (187) located close to the heating element. When nosubstrate is present, air may flow from the fan through the heatingelement, through the air-knife and then directly to the exhaust (197).When a substrate is present, the air flows along the top surface of thesubstrate. In an embodiment, a pre-heating stage (189), for example aninfra-red emitter, heats the substrate prior to the air-knife. Thepre-heat temperature is controlled by an electronic controller (190) anda temperature sensor (191) with an optional safety over-heat sensor(192). In another embodiment, a flat plate attached to the leading edgeof the air-knife forms a pre-heat chamber (189) with the top surface ofsubstrate. This pre-heat chamber traps the hot air close to thesubstrate surface for a longer period allowing the hot air more time topre-heat the substrate surface. A post-heating stage (193), for examplean infra-red emitter (190) located subsequent to the air-knife providesadditional heat that can extend the time that the substrate stays at anelevated temperature. The post-heating temperature is controlled by anelectronic controller (194) and a temperature sensor (195), with anoptional safety over-heat sensor (196). In another embodiment, there isa heating element in place of the pre-heat chamber. The pre-heating ofthe substrate can serve to reduce thermal stress during the very rapidheating under the air-knife and to provide an additional control on thepeak temperature the substrate reaches under the air-knife, the peaktemperature being a function of the initial temperature plus thetemperature rise due to the air-knife.

A major advantage of this embodiment of a skin-cure system is that itallows the curing of a thin-film sol-gel coating without heating theentire substrate to a high temperature. A properly configured air-knifeis able to heat the surface very fast (high power) without imparting agreat deal of heat (energy) to the full substrate. Thus while thesurface heats rapidly to a high temperature the overall substrate doesnot heat up excessively. In one embodiment the substrate is glass coatedon one side with thin-film solar cells, and the opposing side of theglass is the desired surface for the sol coating. In this case, it isdesirable to avoid heating and raising the temperature of thesemiconductor photovoltaic material as much as possible while curing thesol coating. Thin-film solar materials such as CdTe, CIGS or amorphoussilicon can be quite sensitive to elevated temperatures. Hightemperatures can cause dopants within the material to defuse in adetrimental manner or can cause metal electrode materials to defuse intothe photovoltaic material. In some embodiments, the temperature of thephotovoltaic cell may be kept from exceeding 100° C. to 120° C. as thesol is cured. Additionally, polymer materials within the finished solarmodule such as encapsulates may be kept from exceeding their glasstransition temperature of 150° C. to 200° C.

FIG. 18 shows an example temperature profile for a skin-cure system. Inthis example the substrate is a dummy thin-film solar module consistingof two pieces of glass typical of those used in thin-film modulemanufacturing, laminated together with temperature sensors embeddedbetween the glass sheets such that they measure the interior temperatureof the dummy module and temperature sensors attached to the top surface.The module is moved at a speed of 1 cm/s under an air-knife set to anexit air temperature of approximately 650° C. and a gap distance (fromsubstrate top surface to the air-knife opening) of approximately 1 cm.Two temperatures are shown, the top surface temperature representing thetemperature reached by the interior of the dummy module. In this examplethe pre-heat chamber embodiment was used. From the profile, the pre-heatchamber caused an initial rise in temperature of the top surface (202)to approximately 100° C., there after the air-knife caused a very rapidtemperature rise (200) to approximately 300° C. after which thepost-heat infra-red emitter set to a temperature of 300° C. as measuredby a sensor placed between the substrate and the IR emitter, maintainsthe top surface temperature (201) at approximately 200° C. Through-outthe process the interior temperature never exceeds approximately 90° C.

In one embodiment, the substrate is glass of thickness 1 mm to 4 mm. Inan embodiment of a skin-cure apparatus, the air-temperature exiting theair knife is between 500° C. to 750° C. as controlled by the powersetting of the heating element and the volume of air provided by thefan. The speed of the substrate is between 0.25 cm/s and 3.5 cm/s. Theresulting temperature of the substrate surface is between 150° C. to600° C. and this temperature is attained between the start of thepre-heat chamber and the end of the air-knife. In other embodiments thesubstrate is pre-heated by an infra-red emitter to approximately 25° C.to 200° C. prior to the air-knife wherein it is further heated toapproximately 150° C. to 600° C. Thereafter, the substrate is maintainedat a temperature of between 120° C. to 400° C. until the end of thepost-heat section. Such a configuration of the skin-cure apparatus hasbeen shown to cure the sol coating while leaving the opposing surface ata temperature below 120° C.

The process of rapidly heating the substrate using the air-knife andthen maintaining that temperature with radiant heat facilitates thecuring of the sol-gel material. In an embodiment, the curing is achievedby providing sufficient energy so that a sufficient portion of theremaining Si—OH moieties within the coating undergo a condensationreaction and form Si—O—Si crosslinks that greatly strengthen thematerial enabling it to pass Taber abrasion testing to standard EN1096.2with no more than 0.5% loss of absolute transmission. In otherembodiments, the curing temperature is used to facilitate otherprocesses such as volatizing a sacrificial component of the coating toform a desired porosity or a desired surface morphology. Otherembodiments may use very high temperatures to completely oxidize allorganic components in the coating creating a hydrophilic pure silicafilm. Yet further embodiments may use the heat and/or reactive gascomposition of the air-knife to initiate chemical reactions that modifythe properties of the coating, such as for example, surface energy,color, refractive index, surface morphology and surface chemistry. Inembodiments, the skin-cure process works in concert with the compositionand properties of the coating material to facilitate tuning of theproperties of the final thin-film coating.

The foregoing apparatus and methods are particularly well suited to theapplication of sol-gel thin-films to glass. In an embodiment, the glassto be coated is the front (sun facing) surface of a solar module and thesol-gel thin-film is an anti-reflective coating. Either bare glass maybe coated and/or cured by the apparatus or fully assembled solar modulesor solar modules at any intermediate stage of manufacture. In otherembodiments, the apparatus may be used to coat and/or cure windows,architectural glass, displays, lenses, mirrors or other electronicdevices.

In an aspect, a coating and curing apparatus may include a conveyorsystem of a combination roll coating and curing facility, wherein thecombination roll coating and curing facility comprises at least one rollcoating facility and at least one curing facility, and wherein theconveyor system is adapted to transport a substantially flat substratethrough the combination roll coating and curing facility, a processorthat controls a process parameter of the at least one roll coatingfacility, and an air knife of the at least one curing facility, whereinthe air knife is adapted to direct heated air to a portion of the flatsubstrate as it is transported through the at least one curing facility,wherein the at least one roll coating facility is adapted to coat thesubstantially flat substrate with a sol gel coating material. Thesubstantially flat substrate may be a part of at least a partiallyfinished solar module. The apparatus may further include an electricalelement disposed within the air stream to heat the air flowing throughthe air knife. The air may be heated to a temperature between about 300°C. and 1000° C. The apparatus may further include a fan in the airstream that directs air to the air-knife. The apparatus may furtherinclude an electronic controller that controls the temperature based onreadings from at least one temperature sensor located in the air stream.The apparatus may further include an exhaust to remove heated air fromthe apparatus. The apparatus may further include a flat plate attachedto the leading edge of the air-knife, wherein the flat plate is adaptedto form a pre-heat chamber with the top surface of the substantiallyflat substrate. The apparatus may further include an infra-red emitterdisposed along the conveyor system prior to the air knife, wherein theinfra-red emitter is adapted to heat the substantially flat substrate toa temperature of between 25° C. to 200° C. The apparatus may furtherinclude an infra-red emitter disposed along the conveyor systemsubsequent to the air knife, wherein the infra-red emitter is adapted tomaintain the flat substrate at a temperature of between 120° C. to 400°C. The process parameters may include at least one of a doctor rollerspacing and/or pressure to an application roller, the application rollerspacing or pressure taken with respect to the substantially flatsubstrate, a speed at which the substantially flat substrate is conveyedby the conveyor system, and in the case of reverse roll-coating, adifference in speed between the substantially flat substrate and theapplication surface of the application roller. The processor may furthercontrol a process parameter of the curing facility. A plurality of rollcoating facilities and curing facilities may be arranged sequentially.The air-temperature exiting the air knife may be between 500° C. to 750°C. The speed of the substantially flat substrate on the conveyor systemmay be between 0.25 cm/s and 3.5 cm/s. The resulting temperature of asurface of the substantially flat substrate may be between 150° C. to600° C.

In an aspect, a method of coating and curing may include conveying asubstantially flat substrate to be coated with a conveyor system througha combination roll coating and curing facility, wherein the combinationroll coating and curing facility comprises at least one roll coatingfacility and at least one curing facility, roll coating thesubstantially flat substrate with a sol gel coating material with the atleast one roll coating facility, and curing the sol gel coating materialon the substantially flat substrate with an air knife of the at leastone curing facility, wherein the air knife is adapted to direct heatedair to a portion of the substantially flat substrate as it istransported through the curing facility by the conveyor system. Asol-gel coated substantially flat substrate may be formed by the method,wherein a portion of the sol-gel coating material is cured while adifferent portion of the sol-gel coating material remains uncured.

In an aspect, a method of tuning the performance of a sol gel coatingmay include determining a desired cure temperature profile to achieve aspecific performance metric for a sol gel coating using at least onephysical analysis method, selecting settings for an air knife curingsystem's operating parameters to achieve the desired temperatureprofiles for the sol gel coating on a substantially flat substrate, andcuring the sol-gel coating on the substantially flat substrate with theair knife curing system. The at least one physical analysis method mayinclude at least one of thermogravimetric analysis, Fourier transforminfrared spectroscopy, ellipsometry, nanoindentation, abrasion testing,spectrophotometry, and a water contact angle measurement. The air knifecuring system operating parameters may include at least one of substratespeed, air knife air-flow volume, air knife output air temperature, airknife opening distance to substrate surface, a temperature set-point fora pre-heating zone and a temperature set point for a post heating zone.The performance metric for the sol-gel coating may include at least oneof hardness, abrasion resistance, surface energy, refractive index,optical transmission, thickness and porosity. The method may furtherinclude a step of coating the substantially flat substrate with the solgel coating using a roll-coating system before the step of curing. Asol-gel coated substantially flat substrate may be formed by the method.The specific performance metric may include a hardness of the sol-gelcoating within a range of 0.2 GPa to 10 GPa. The specific performancemetric may include a test in which no more than 1% of absolute opticaltransmission is lost after at least 500 strokes of an abrasion testperformed in accordance with specification EN1096.2. The specificperformance metric may include a water contact angle where the watercontact angle is within 60° to 120°. The specific performance metric mayinclude a water contact angle where the water contact angle is within 5°to 30°. The specific performance metric may include a refractive indexof the cured, coated sol gel from 1.25 to 1.45. The thickness may beapproximately 50 nm to 150 nm. A sacrificial component of the sol-gelcoating may be volatilized to form a desired porosity.

FIG. 19 shows a thermogravimetric analysis of representative samples ofcoating material. Thermogravimetric analysis is performed by heating asample gradually and recording the loss of mass as various components ofthe sample volatilize. When performed on coating materials such as theseexample sol-gel coatings for glass, it can be used to determine criticaltemperatures required to cure the coating material. The figure showsthree temperatures of interest. Using Sample 1 from Example 3 in FIG. 19as an illustrative example, there is a point of inflection (210) atapproximately 125° C., another much steeper point of inflection (211) atapproximately 450° C. finally there is a flattening out (212) above 500°C. Without being bound by theory, these three points are interpreted asfollows. As temperature increases to point 210 any residual water andsolvent is volatilized and all easily accessible Si—OH moieties react,condense and release water. This represents a cured film that hasattained a useful hardness and abrasion resistance at a relatively lowtemperature. Further heating in the range from point 210 until point 211represents an approximately linear reduction in mass as additionalremaining Si—OH moieties condense and release water. This temperaturerange represents increasing hardness and abrasion resistance of thematerial with increasing temperature, without detrimental effects on thecoating. This reduction in mass causes a corresponding decrease indensity and hence a decrease in refractive index.

In coating materials that form hydrophobic films, the reduction in Si—OHmay also result in an increase of the hydrophobic effect as measured byincreasing water contact angle. Heating beyond point 211 begins tooxidize organic moieties within the coating and decomposes the material,the byproducts of which may then volatilize. In some embodiments thesemoieties may be methyl groups or other hydro-carbon groups orfluoro-carbon chains or any combination thereof. Other reactions mayalso occur such as for example the formation of SiC andSi_(x)O_(y)C_(z). This temperature regime may be generalized as theoxidation of the organic components of the coating, reactions betweenbyproducts of that oxidation with each other and with components of thefilm itself and the transformation of the coating to a substantiallyinorganic silica coating. At this point further heating no longer causessignificant mass loss and the curve flattens out as indicated by point212. Sample 2 of example 2 exhibits approximately the same shape andinflection points as Sample 1. It also illustrates that when morecomplex organic moieties are present in the coating the transformationthat occurs after the second inflection point can be more complex andmore prolonged. Therefore, for the purposes of developing a process forcuring these coatings we can determine from this analysis that a firstlow temperature cure can be accomplished at a temperature ofapproximately 125° C., which is the first point of inflection. A secondhigher temperature cure at the second point of inflection (approximately450° C. for the material in Sample 1 and 350° C. for the material inSample 2) results in increased hardness, abrasion resistance andhydrophobicity. Temperatures beyond the second inflection point resultin the breakdown and modification of organic moieties that may in someembodiments be useful.

The curing process parameters including substrate speed, air knifeoutput air temperature, air knife air flow volume, air knife openingdistance to substrate surface, pre and post heating set temperatures areused to control process cure parameters including maximum temperature,rate of heating, duration at temperature, cumulative temperatureexposure and rate of cooling that can be used to tune specificproperties of the final cured film. One property is hardness as measuredby nano-indentation methods. In some embodiments, the curing systemdescribed herein may cure sol-gel coatings on glass substrates to ahardness of approximately 0.2 GPa to 10 GPa and preferably to a hardnessof approximately 2 GPa to 4 GPa. Another property is abrasionresistance. In some embodiments, the curing system described herein maycure sol-gel coatings on glass substrates to an abrasion resistancewhereby they lose no more than 1% of absolute optical transmission asmeasured by spectrophotometer after 500 strokes of an abrasion testperformed in accordance with specification EN1096.2 and preferably nomore than 0.5% loss of absolute optical transmission after 1000 strokes.Such a test can be performed using a Taber reciprocating abrader model5900 with a ratcheting arm assembly. A third property is surface energyas measured by water contact angle (WCA). In some embodiments the curingsystem described herein may cure sol-gel coatings to a WCA ofapproximately 60° to 120° and preferably to a WCA of approximately 70°to 100°. In other embodiments the film can be cured to a WCA ofapproximately 5° to 30° and preferably a WCA of approximately 10° to20°. A fourth property is refractive index (RI) as measured byellipsometer. In some embodiments the curing system described herein maycure sol-gel coatings to a RI of approximately 1.25 to 1.45 andpreferably a RI of approximately 1.35 to 1.42. A fifth property is finalfilm thickness as measured by ellipsometer. The final film thickness isa function of the initial (pre-cure) dry film thickness and the cureparameters such that the cure parameters modify the initial drythickness. In some embodiments the curing system described herein maycure sol-gel coatings to a thickness of 50 nm to 150 nm and to apreferred thickness of 70 nm to 130 nm.

FIGS. 20 a, 20 b and 20 c depict data for an exemplary sol-gel coatingthat demonstrate control of final film thickness, refractive index andwater contact angle as a function of maximum cure temperature.

FIG. 20 d shows Fourier transform infrared spectra (FT-IR) of sol-gelcoating material from Example 3 taken before and after a cure processstep. This analysis technique shows how chemical bonds within thematerial change during the curing process. In particular, the spectralpeaks denoted by points 220, 221 & 222 have changed during the process.Without being bound by theory, these changes can be interpreted as thereduction of Si—OH bonds through condensation causing the reduction ofthe peaks at points 220 and 222. These bonds are converted to Si—O—Sibonds causing the increase in the peak at point 221. This analysistechnique can be used to quantify the proportion of Si—OH bonds thatcondense and hence to quantify the degree to which the film is cured.FIG. 20 e shows FT-IR spectra of Example 3 cured at different curetemperatures of 120° C., 200° C. and 400° C.

FIG. 21 shows Si-29 NMR of the sol from Example 2 taken before coatingand curing. The assigned chemical shifts and qualitative mol % of totalmolecules are shown in Table 14.

TABLE 14 The list of assigned peaks and mol % of total molecules in FIG.21. Chemical mol % of unit in the Si signal in unit Structure shifts/ppmtotal sol structure [RSi(OH)₂O_(0.5)]_(a) and [R′Si(OH)₂O_(0.5)]_(m) −536.22 [RSi(OH)O]_(c) and [R′Si(OH)O]_(p) −58 10.46 [RSiO_(1.5)]_(b) and[R′SiO_(1.5)]_(n) −63.3 40.49 [Si(OH)₃O_(0.5)]_(z) −90 2.73[Si(OH)₂O]_(y) −93 2.0 [Si(OH)O_(1.5)]_(x) −99.65 27.21 [SiO₂]_(w)−108.52 10.43

Total Si—OH containing units in the sol of Example 2 is 48.6 mol % ofunits of the total sol structure based in Si-NMR. However, not all Si—OHhave the same reactivity towards condensation as some have more sterichindrance than others in the complex cage, branch and network structureof the sol polymer.

FIG. 22 shows Si-29 NMR of the sol from Example 3 taken before coatingand curing. The assigned chemical shifts and qualitative mol % of totalmolecules are shown in Table 15.

TABLE 15 The list of assigned peaks and mol % of total molecules in FIG.22. Chemical mol % of unit in the Si signal in unit Structure shifts/ppmtotal sol structure [RSi(OH)₂O_(0.5)]_(a) −53 11.11 [RSi(OH)O]_(c) −581.00 [RSiO_(1.5)]_(b) −63.3 41.38 [Si(OH)₃O_(0.5)]_(z) −90 2.73[Si(OH)₂O]_(y) −93 2.0 [Si(OH)O_(1.5)]_(x) −99.65 30.27 [SiO₂]_(w)−108.52 11.74

Total Si—OH containing units in the sol of Example 3 is 47.1 mol % ofunits of the total sol structure based in Si-NMR. However, not all Si—OHhave the same reactivity towards condensation as some have more sterichindrance than others in the complex cage, branch and network structureof the sol polymer.

FIG. 30 a is a top-down SEM micrograph of a sample roll-coated with asingle-layer transparent coating from the solution from Example 55. Itdepicts a plurality of voids in the coating. FIG. 30 b is the result ofan image analysis of the SEM micrograph of FIG. 30 a using the opensource ImageJ program. It shows the distribution of void diameter forvoids open and or visible at the surface of the film in the image. Inthis particular embodiment, the distribution is bi-modal, with a firstgroup of voids having a mean diameter of about 119 nm and a standarddistribution of about 28 nm and a second group having a mean diameter ofabout 387 nm and a standard distribution of about 32 nm. In embodimentsof the present disclosure, coatings may have bi-modal distributions ofvoid diameter with a first group having a mean of between about 25 nmand about 150 nm and a standard deviation of between about 5 nm andabout 40 nm, and a second group having a mean of between about 150 nmand about 500 nm and a standard deviation of between about 25 nm andabout 50 nm.

FIGS. 31 a-36 a are top-down SEM micrographs of samples prepared fromembodiments of the present disclosure that have approximately Gaussiandistributions of void diameter as determined by image analysis of themicrograph images with the ImageJ software program. They show thedistribution of void diameter for voids open and or visible at thesurface of the film in the image. FIG. 31 b shows a distribution with amean void diameter of about 49 nm with a standard deviation of about 7nm. FIG. 32 b shows a distribution with a mean void diameter of about 57nm with a standard deviation of about 9 nm. FIG. 33 b shows adistribution with a mean void diameter of about 69 nm with a standarddeviation of about 10 nm. FIG. 34 b shows a distribution with a meanvoid diameter of about 37 nm with a standard deviation of about 4 nm.FIG. 35 b shows a distribution with a mean void diameter of about 113 nmwith a standard deviation of about 15 nm. FIG. 36 b shows a distributionwith a mean void diameter of about 119 nm with a standard deviation ofabout 15 nm. In embodiments of the present invention coatings may haveapproximately Gaussian distributions of void diameter between about 10nm and about 150 nm with standard deviations of about 2 nm to about 40nm and between about 35 nm and about 120 nm with standard deviations ofbetween about 4 nm and about 15 nm.

Using the void area data generated from the ImageJ analysis of FIGS. 30a-36 a, the percentage of the surface area that is visible open voidscan be determined. Table 16 below summarizes the area percentages forthe figures shown.

TABLE 16 Percentage of total area that is visible voids at the surface.FIG. % 30 9.5% 31 5.7% 32 5.9% 33 7.2% 34 3.2% 35 13.4% 36 19.3%

In embodiments of the present disclosure, coatings, which may besingle-layer transparent coatings, may have ratios of total area ofvoids visible at the surface to total surface area of between about 1%and about 50% and between about 3% and about 20%.

FIGS. 37 a, 37 b, 37 c and 37 d are oblique cross-sectional SEMmicrographs of embodiments of the present disclosure of coatings, whichmay be single-layer transparent coatings, showing a cross-sectionthrough the coating and part of the top surface of the coating. Thecoating may contain a plurality of oblate voids. The size of the voidsmay range from small to large relative to the thickness of the coating.In embodiments the ratio of the void major axis to the average thicknessof the coating is between about 0.05 to about 5. In embodiments somevoids may substantially extend through the full thickness of thecoating. In embodiments, some voids may be open to the surface. Inembodiments, some voids may not be open to the surface. In embodiments,the vertical distribution of voids through the thickness of the coatingmay be bi-modal with a first group of relatively smaller voids withinthe bulk of the coating and a second group of relatively larger voidsopen to the surface of the coating. Open voids at the surface of thecoating may also be characterized as dimples, depressions, holes or thelike. In embodiments, the vertical distribution of voids through thethickness of the coating may be approximately Gaussian.

For characterization purposes, the porosity of the coating may bedefined as the percentage of the total cross-sectional area of thecoating that is within visible voids in a cross-sectional SEM micrographof the coating. In embodiments the porosity of the coating may bebetween about 50% and about 2% and between about 30% and about 5%.

In embodiments, the major axis of the oblate voids in the coating may bebetween about 5 nm and about 500 nm and between about 150 nm and about250 nm and between about 5 nm and about 100 nm and between about 40 nmand about 80 nm. The minor axis of the oblate voids may be between about3 nm and about 150 nm and between about 70 nm to about 90 nm and betweenabout 20 nm to about 60 nm and between about 3 nm and about 50 nm. Theflattening or ellipticity, or oblateness of the oblate voids may bedefined with the following equation where a is the major axis and b isthe minor axis.

$f = \frac{a - b}{a}$

In embodiments, the oblate voids in the coating have a flattening ofbetween about 0.0 to about 0.8 and between about 0.3 to about 0.7.

FIG. 38 illustrates the transmittance spectra of a piece of PPGStarphire float-glass coated with the mixture of Example 55 versus thetransmittance spectra of a the same glass type that is uncoated. Thesample shows a strong anti-reflective effect with ΔT_(AM) (absolutedifference in solar weighted transmission between coated and uncoated)of 2.74%.

The presence of relatively large voids in the coating may engenderseveral useful properties to the coating and to articles to which thecoating is applied. In some embodiments, the porosity of the coating,which may be a single-layer transparent coating, reduces its refractiveindex such that the coating acts as a very effective anti-reflectinglayer. In some embodiments the bi-modal distribution of voids in thecoating may be used to create more complex optical transmission spectracompared to the spectra of a single-layer anti-reflective coating; thelarger voids may be sized such that they scatter short wavelength UVlight while not substantially affecting longer wavelength light, whilesmaller voids would have negligible scattering effects but would reducethe coating refractive index to enhance anti-reflective performance.Such coatings may be very useful in applications such as solarphotovoltaic modules wherein maximum transmission of solar light isdesired, but at the same time materials within the photovoltaic modulesuch as encapsulants like EVA and backsheet materials may be degraded byUV light. Another useful application would be so-called conservationglass wherein art works or other artifacts need to be displayed behindglass, but it is desired to reduce reflections from the glass for easyviewing while at the same time filtering harmful UV light that maydamage or degrade the art works or artifacts over the longer term. Todaysuch conservation glass is fabricated using multiple coating layers withseparate functions such as UV filtering and anti-reflection andanti-fingerprint or anti-stain. The coating of the present invention mayhave all of these functions in a single layer. In some embodiments thevoids may be used to hold a substance that can impart additionalproperties in situ or that can be released over time to achieve a usefulgoal. In some embodiments, hydrophobic and oleophobic materials such aslong-chain hydrocarbons, silicone polymers, fluoro-polymers and the likecould be held in the voids so that they imparted a long term hydrophobicand or oleophobic characteristic to the glass surface. In someembodiments, the refractive index of the material within the void maysubstantially match the refractive index of the bulk of the coating andso that even relatively large voids would have negligible opticaleffect. Materials could be deposited into the voids by various methodsof coating known in the art such as roll-coating, spray coating,slot-die coating, dip-coating, emersion and the like. In someembodiments, the voids could be re-charged with material in the fieldafter some period of time, for example by applying a spray or rubbing amaterial on the surface. In some embodiments, the voids could be used tohold biocide materials such as fungicides and pesticides and the like toimpart longer term resistance to bio-contamination. In some embodiments,the size of the voids could be selected such that the release ofsubstances held within the voids was temporally controlled. In someembodiments, the substance within the voids could be a drug or othermedicinal or bio-active agent.

It should be appreciated that reference throughout this specification to“one embodiment” or “an embodiment” means that a particular feature,structure or characteristic described in connection with the embodimentis included in at least one embodiment of the present disclosure.Therefore, it is emphasized and should be appreciated that two or morereferences to “an embodiment” or “one embodiment” or “an alternativeembodiment” in various portions of this specification are notnecessarily all referring to the same embodiment. Furthermore, theparticular features, structures or characteristics may be combined assuitable in one or more embodiments of the disclosure.

Similarly, it should be appreciated that in the foregoing description ofexemplary embodiments of the disclosure, various features of thedisclosure are sometimes grouped together in a single embodiment,figure, or description thereof for the purpose of streamlining thedisclosure aiding in the understanding of one or more of the variousinventive aspects. This method of disclosure, however, is not to beinterpreted as reflecting an intention that the claimed disclosurerequires more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment. Thus, the claimsfollowing the detailed description are hereby expressly incorporatedinto this detailed description, with each claim standing on its own as aseparate embodiment of this disclosure.

While the disclosure has been disclosed in connection with the preferredembodiments shown and described in detail, various modifications andimprovements thereon will become readily apparent to those skilled inthe art. Accordingly, the spirit and scope of the present disclosure isnot to be limited by the foregoing examples, but is to be understood inthe broadest sense allowable by law.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the disclosure (especially in the context of thefollowing claims) is to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the disclosureand does not pose a limitation on the scope of the disclosure unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe disclosure.

While the foregoing written description enables one of ordinary skill tomake and use what is considered presently to be the best mode thereof,those of ordinary skill will understand and appreciate the existence ofvariations, combinations, and equivalents of the specific embodiment,method, and examples herein. The disclosure should therefore not belimited by the above described embodiment, method, and examples, but byall embodiments and methods within the scope and spirit of thedisclosure.

All documents mentioned herein are hereby incorporated in their entiretyby reference. References to items in the singular should be understoodto include items in the plural, and vice versa, unless explicitly statedotherwise or clear from the text. Grammatical conjunctions are intendedto express any and all disjunctive and conjunctive combinations ofconjoined clauses, sentences, words, and the like, unless otherwisestated or clear from the context.

What is claimed is:
 1. A single layer transparent coating with ananti-reflective property, a hydrophobic property that is highly abrasionresistant and; wherein the single layer transparent coating contains aplurality of oblate voids and; wherein at least 1% of the oblate voidsare open to a surface of the single layer transparent coating.
 2. Thecoating of claim 1, wherein a thickness of the single layer transparentcoating is between 10 nm and 5 μm.
 3. The coating of claim 1, wherein arefractive index of the single layer transparent coating is less than1.45.
 4. The coating of claim 1, wherein an average reflection ofvisible light from a surface of glass coated with the single layertransparent coating is less than 3%.
 5. The coating of claim 1, whereina T_(AM) of a coated glass substrate is at least 1% greater than aT_(AM) of a same type of uncoated glass substrate.
 6. The coating ofclaim 1, wherein a water contact angle in a test for the hydrophobicproperty is greater than 70°.
 7. The coating of claim 1, wherein areduction in optical transmission of the single layer transparentcoating as measured by T_(AM) after performance of 1000 strokes ofabrasion testing according to the procedure in standard EN1096.2 is lessthan 1.0%.
 8. The coating of claim 1, wherein a distribution of a voiddiameter of the oblate voids comprises a Gaussian distribution with amean of between 10 nm and 150 nm with a standard deviation between 2 nmand 40 nm.
 9. The coating of claim 1, wherein a distribution of voiddiameter of the oblate voids is bi-modal with a first group having aGaussian distribution with a mean between 25 nm and 150 nm and astandard deviation between 5 nm and 40 nm and a second group having aGaussian distribution with a mean between 150 nm and 500 nm and astandard deviation between 25 nm and 50 nm.
 10. The coating of claim 1,wherein at least 1% of the oblate voids extend through a full thicknessof the single layer transparent coating.
 11. The coating of claim 1,wherein all of the oblate voids are contained within a full thickness ofthe single layer transparent coating.
 12. The coating of claim 1,wherein the surface of the single layer transparent coating has apercentage of visible voids between 1% and 50%.
 13. The coating of claim1, wherein a porosity of the single layer transparent coating is between50% and 2%.
 14. The coating of claim 1, wherein the major axis of theoblate voids in the single layer transparent coating is between 5 nm and500 nm and the minor axis of the oblate voids is between 3 nm and 150nm.
 15. The coating of claim 1, wherein the flattening of the oblatevoids is between 0.0 to 0.8.
 16. The coating of claim 1, wherein thesingle layer transparent coating is cured at a temperature of less than400° C.
 17. The coating of claim 1 further comprising, a glass substratehaving a surface on which said coating is applied.
 18. The coating ofclaim 1 further comprising a solar module having a surface on which saidcoating is applied.